9. Threat: Invasive alien and other problematic species
© Book authors, CC BY 4.0 https://doi.org/10.11647/OBP.0234.09
Background
Invasive and other problematic species of animals, plants and diseases have caused significant declines in many mammal species worldwide. Invasive species may prey on mammals, provide competition for resources, alter habitats or infect mammals with new diseases. This chapter describes the evidence from interventions designed to reduce the threat from invasive and other problematic species and disease.
See also: Species management — Release translocated/captive-bred mammals to islands without invasive predators.
For interventions that involve reducing predation by domestic cats Felis catus and dogs Canis lupus familiaris see the chapter Threat: Residential and commercial development -Keep cats indoors or in outside runs to reduce predation of wild mammals, Use collar-mounted devices to reduce predation by domestic animals, Keep dogs indoors or in outside enclosures to reduce threats to wild mammals and Keep domestic cats and dogs well-fed to reduce predation of wild mammals.
9.1. Use fencing to exclude grazers or other problematic species
https://www.conservationevidence.com/actions/2495
- Three studies evaluated the effects on mammals of using fencing to exclude grazers or other problematic species. One study was in each of the USA1, Australia2 and Spain3.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): A controlled, before-and-after study in Australia2 found that after fencing to exclude introduced herbivores, native mammal species richness increased.
POPULATION RESPONSE (3 STUDIES)
- Abundance (3 studies): Two controlled studies (including one replicated, paired sites study) in Spain3 and Australia2 found that using fences to exclude large3 or introduced2 herbivores increased the abundance of Algerian mice3 and native mammals2. A replicated, paired sites study in the USA1 found that in areas fenced to exclude livestock grazing and off-road vehicles, abundance of black-tailed hares was lower compared to in unfenced areas.
BEHAVIOUR (0 STUDIES)
A replicated, paired sites study in 1994–1995 in the Western Mojave Desert, California, USA (1) found that within an area fenced to exclude livestock grazing and off-road vehicles, abundance of black-tailed hares Lepus californicus was lower compared to unfenced areas. Fewer black-tailed hares were found in fenced plots (0–1.5 animals/transect; 1.5 droppings/1,250 cm2) than in unfenced plots (1–4 animals/transect; 3–4 droppings/1,250 cm2). In the Desert Tortoise Research Natural Area, off-road vehicles were prohibited from 1973, sheep grazing from 1978, and a 1 m high wire fence protecting the area was constructed by 1980. Two sites were selected near the north eastern and southern boundary. At each site, two 2.25-ha plots were established, one ≥400m inside the fenced area and one outside the fence (used by off-road vehicles until 1980 and grazed by sheep until 1994). Plots were matched for environmental variables. In each plot, hare numbers were estimated along four 1.2-km transects in May and July 1994, and at the north eastern site by counting pellets in 120 quadrats (40 × 50-cm) in April 1994 and 1995.
A controlled, before-and-after study in 2004–2007 in a woodland savannah in north-west Australia (2) found that after fencing to exclude introduced herbivores, the overall abundance and species richness of small-and medium-sized native mammals increased. After three years, the average number of mammals and mammal species/ plot was higher in sites from which introduced herbivores were excluded (abundance: 6.1–16.7 animals; species richness: 2.5–3.2 species) than in non-removal sites (abundance: 0.1–3.3 animals; species richness: 0.1–1.4 species). Overall abundance varied with habitat type and abundance increased with years since destocking for four of seven species (see original paper for details). In 2004–2005, a 40,300-ha area of Mornington Wildlife Sanctuary was fenced and cleared of large herbivores. Before 2004, the area had >2,000 cattle Bos taurus and >200 horses Equus ferus caballus and donkeys Equus africanus asinus. In 2007, less than 200 cattle remained. Native mammals were surveyed in twenty 0.25-ha plots in 2004 and in 42–43 plots annually in 2005–2007 (total 49 separate plots, most surveyed 3–4 times). By 2006 and 2007, sixteen plots still contained herbivores, and herbivores had been removed from the other plots (1–3 years previously). Each plot was surveyed using 20 box traps, four medium-sized cage traps and eight pitfall traps, for three consecutive nights each year. Fur was clipped to exclude recaptures.
A replicated, controlled, paired sites study in 2010–2012 in Holm oak Quercus ilex woodland in Cabañeros National Park, Central Spain (3) found that excluding large herbivores using fences increased the abundance of Algerian mice Mus spretus. The abundance of Algerian mice and the percentage of trees occupied by mice were higher inside exclosures (103 individuals caught; 60% of trees occupied) than outside (55 individuals caught; 30% of trees occupied). However, mice had higher levels of physiological stress indicators (faecal corticosterone metabolites) inside (33,041 ng/g dry faeces) than outside exclosures (29,225 ng/g). One 3 ha section of a 150 ha exclosure established in 1995 and a 4.7 ha exclosure established in 2008 were paired with grazed areas of equal size. Exclosures were fenced (2 m high) with a 32 x 16 cm mesh width that allowed movement of rodent predators but not of large herbivores. Mice were sampled during two consecutive nights in November 2010 and 2011 and February 2011 and 2012 using two Sherman traps placed under all 170 trees in the study sites. Fresh faecal samples from 92 different captured individuals were used to monitor faecal corticosterone metabolites.
(1) Brooks M. (1999) Effects of protective fencing on birds, lizards, and black-tailed hares in the western Mojave Desert. Environmental Management, 23, 387–400.
(2) Legge S., Kennedy M.S., Lloyd R.A.Y., Murphy S.A. & Fisher A. (2011) Rapid recovery of mammal fauna in the central Kimberley, northern Australia, following the removal of introduced herbivores. Austral Ecology, 36, 791–799, https://doi.org/10.1111/j.1442-9993.2010.02218.x
(3) Navarro-Castilla, Á., Diaz, M., & Barja, I. (2017). Does ungulate disturbance mediate behavioural and physiological stress responses in Algerian mice (Mus spretus)? A wild exclosure experiment. Hystrix, 28, 283–291.
9.2. Use fencing to exclude predators or other problematic species
https://www.conservationevidence.com/actions/2497
- Ten studies evaluated the effects on mammals of using fencing to exclude predators or other problematic species. Four studies were in Australia2,3,8,10, four were in the USA4,6,7,9 and two were in Spain1,5.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): A site comparison study in Australia3 found that fencing which excluded feral cats, foxes and rabbits increased small mammal species richness.
POPULATION RESPONSE (10 STUDIES)
- Abundance (4 studies): Two of three of studies (including two replicated, controlled studies), in Spain1, Australia3 and the USA4, found that abundances of European rabbits1 and small mammals3 were higher within areas fenced to exclude predators or other problematic species, compared to in unfenced areas. The third study found that hispid cotton rat abundance was not higher with predator fencing4. A replicated, controlled study in Spain5 found that translocated European rabbit abundance was higher in fenced areas that excluded both terrestrial carnivores and raptors than in areas only accessible to raptors.
- Reproductive success (1 study): A replicated, controlled study in USA9 found that predator exclosures increased the number of white-tailed deer fawns relative to the number of adult females.
- Survival (7 studies): Four of six studies (including four replicated, controlled studies) in Spain1, Australia2,8,10 and the USA4,6, found that fencing to exclude predators did not increase survival of translocated European rabbits1, hispid cotton rats2, southern flying squirrels6 or western barred bandicoots10. The other two studies found that persistence of populations of eastern barred bandicoots2 and long-haired rats8 was greater inside than outside fences. A controlled, before-and-after study in the USA7 found that electric fencing reduced coyote incursions into sites frequented by black-footed ferrets.
BEHAVIOUR (0 STUDIES)
Background
Predators can drive declines or local extinctions of vulnerable mammal species. Non-native predators may be a particular problem for native mammals that lack sufficient predator avoidance behaviours (e.g. Jones et al. 2004). Native predators can also threaten populations of mammals that persist in low numbers. Predator control may be impractical to sustain on a sufficient scale or may attract opposition on animal welfare grounds. Fencing, including electric fencing, may be a viable or more effective alternative in some situations.
See also Species Management — Release translocated mammals into fenced areas and Release captive-bred mammals into fenced areas.
Jones M.E., Smith G.C. & Jones S.M. (2004) Is anti-predator behaviour in Tasmanian eastern quolls (Dasyurus viverrinus) effective against introduced predators? Animal Conservation, 7, 155–160, https://doi.org/10.1017/s136794300400126x
A replicated, controlled study in 2002–2003 in four grassland and shrubland sites in south-west Spain (1) found that the survival of translocated European rabbits Oryctolagus cuniculus was similar between a plot fenced to exclude predators and an unfenced plot, but that abundance was higher in fenced plots. Three months after translocation, rabbit survival in fenced plots (40%) was not significantly different to survival in unfenced plots (57%). However, four months after translocation, the relative abundance of rabbits was higher in fenced than in unfenced plots (data presented as log pellet abundance/plot). Four translocation plots (>1 km apart), each 4 ha with 18 artificial warrens surrounded by low fencing, were established in the south of Sierra Norte of Seville Natural Park. Two plots were fenced (1 m below and 2.5 m above ground, with an electric wire on top) and two unfenced. A total of 724 wild rabbits were released in similar numbers into each plot distributed evenly between warrens. Rabbit survival was based on 45 radio-collared rabbits (19 in one fenced and 26 in one unfenced plot) located 5–7 times/week for 15 weeks. Abundance was estimated four months after translocation by counting pellets in ten 18-cm-diameter circles/warren.
A review of translocation studies in 1989–2005 in eight grassland and forest sites in Victoria, Australia (2) found that translocated eastern barred bandicoot Perameles gunnii populations released inside predator barrier-fencing persisted more successfully than did those translocated into unfenced areas. All three populations translocated into fenced areas persisted at the end of the study (1–26 years post-release). Only one out of five populations translocated to unfenced areas was known to persist at the end of the study (6–13 years post-release). Two populations were presumed extinct and the status was unclear, but with few recent records, at two other sites. Between 22 and 174 bandicoots were translocated into three fences sites (100–585 ha) and between 50 and 103 into five unfenced sites (85–500 ha) in 1989–2005. Translocated animals were both captive-bred and wild-born. Five sites had community involvement with the control of invasive red foxes Vulpes vulpes. Released bandicoots were provided with supplementary food for up to 10 days, in at least two sites. In most sites, bandicoots were monitored by trapping, but frequency and methods are not described.
A site comparison study in 1993–2007 on a shrubland site in South Australia (3) found that using fencing to exclude feral mammals (cats Felis catus, foxes Vulpes vulpes and rabbits Oryctolagus cuniculus) increased the abundance and species richness of small mammals. Small mammal abundance in the absence of feral mammals (10.3 individuals/sample) was higher than where feral mammals were present (3.6 individuals/sample). Species richness followed a similar pattern (feral mammals absent: 3.0 species/sample; feral mammals present: 1.7 species/sample). An area of approximately 5 × 5 km was fenced to exclude feral mammals and cattle in 1999. An adjacent area, approximately 9× 9 km, was fenced in 1986 to exclude cattle, but not feral mammals. Small mammals were sampled using pitfall traps for a 10-day period in either December or January. Three points in the feral mammal and cattle exclosure were sampled in 2007. Five points in the cattle-only exclosure were sampled in 1993–1996 and again in 2007.
A replicated, randomized, controlled study in 2005–2009 in eight woodland sites in Georgia, USA (4) found that excluding predators did not increase survival, transition to reproductive states or abundance of hispid cotton rats Sigmodon hispidus. In non-fire periods, estimated 13-week survival in exclosures (0.16–0.39) were similar to that outside exclosures (0.16–0.38). The same pattern applied in fire periods (exclosures: 0.02–0.04; outside exclosures: 0.02–0.04). Rates of transition to reproductive states varied considerably with season and fire status but were not affected by predator exclusion (exclosure: 0.06–0.59; outside exclosure: 0.06–0.59). Averaged across all plots, predator exclusion did not change abundance (data not presented). Eight plots (40 ha each) were studied. Four were exclosures, with electric fencing to deter predator entry, and four were unfenced. All plots were burned in February 2005, 2007, and 2009. Pairs of grids were live-trapped four times/year from January 2005 to June 2007 and eight times/year from July 2007 to June 2009.
A replicated, controlled study in 2010 at a site in Sierra Morena, Spain (5) found that the abundance of translocated European rabbits Oryctolagus cuniculus was higher in areas fenced to exclude both terrestrial carnivores and raptors (top-closed) than in areas only accessible to raptors (top-open) during the six weeks after release. The weekly abundance of rabbits in top-closed plots (1.2–4.8 pellet abundance index) was higher than in top-open plots (0.7–3.2 pellet abundance index). The highest difference in rabbit abundance between top-closed and top-open plots was attained in the first 2 weeks. Five 0.5-ha plots, close together, were fenced (0.5 m below and 2 m above the ground with two electric wires and a floppy overhang) to exclude terrestrial carnivores. Each had five artificial warrens. Two plots had top net (top-closed) and three had no top net (top-open). Twenty-five adult wild rabbits (20 female) were released in each exclosure in February 2010. Rabbit abundance was estimated through pellet counts in 20 fixed 0.5-m2 circular sampling sites each week for six weeks after translocation.
A replicated, controlled study in 2005–2009 in four woodland sites in Georgia, USA (6) found that using fencing to exclude predators did not increase survival of southern flying squirrels Glaucomys volans. Monthly survival rates for squirrels was similar in areas that were fenced to exclude predators and areas that were not fenced (data reported as model results). Four plots were fenced with a 1.2-m tall, electrified, fence while four plots were not fenced. Plots were 36–49 ha. One-hundred and forty-four traps baited with oats and bird feed were placed on the ground in each plot and 24 traps were placed in trees. Between January 2005 and June 2007, trapping was carried out four times a year and, in July 2007–September 2009, trapping was carried out eight times a year. Trapping was conducted over four consecutive nights. Animals caught were marked with ear tags.
A controlled, before-and-after study in 2010 at a grassland in Montana, USA (7) found that electric fencing reduced coyote Canis latrans incursions into black-tailed prairie dog Cynomys ludovicianus colonies that supported breeding black-footed ferrets Mustela nigripes. There was a lower rate of coyote incursions with the fence in place (four incursions during 84 search nights — 7% of coyote sightings during this period) than before it was installed (eight from 24 search nights — 42% of sightings) and after it was removed (20 from 34 search nights — 47% of sightings). Black-footed ferrets were reintroduced to the site in 1994. Two electric (electronet) fences, totalling 7.7 km and enclosing 108 ha, were erected on 27 July 2010 and removed on 2 October 2010. Fencing comprised nine horizontal poly-conductors, 10 cm apart, alternating between grounded and charged. Conductive polytape (2 cm wide) was strung above this at 107 cm high. Coyote sightings were noted inside fenced areas and in two unfenced areas during spotlight ferret surveys from 28 June to 26 July (pre-exclosure), 27 July to 2 October (exclosure) and 3 October to 24 October (post-exclosure). Coyotes found inside exclosures were expelled through temporarily lowered fence sections.
A replicated, paired sites, controlled study in 2011–2013 in two tropical savanna sites in the Northern Territory, Australia (8) found that fencing to exclude cats Felis silvestris catus prevented the local extirpation of released long-haired rats Rattus villosissimus. After 18 months, rats persisted in enclosures not accessible to cats (3.1–8.7 rats/enclosure) but were absent in compartments accessible to cats (0.0 rats/enclosure). Two 12.5-ha enclosures were established 13 km apart in Wongalara Wildlife Sanctuary. One half of each enclosure was surrounded by a 0.9-m-high fence that allowed access to cats and dingoes Canis dingo and the other half by a 2-m electrified ‘floppy-top’ fence that excluded cats and dingoes. Enclosures had a 40-cm barrier that prevented rats from moving in or out. Fifteen to 23 long-haired rats were introduced to each of the four compartments in October 2011 or April 2012. Rat abundance was monitored until June 2013 by live-trapping at two-month intervals (from 2 or 6 months after release) using 36 box traps in each compartment, deployed over 2–4 consecutive nights.
A replicated, controlled study in 2011–2012 of a forest in Georgia, USA (9) found that predator exclosures increased the fawn:adult female ratio of white-tailed deer Odocoileus virginianus. The average annual fawn:adult female ratio recorded was greater inside exclosures (0.19) than outside (0.09) exclosures. Authors reported that figures were relative rather than absolute ratios, as some fawns may have been too small to travel with their mothers at the time of sampling. Four 40-ha plots were fenced to exclude predators. The fence was 1.2 m tall and was electrified. Predators inside exclosures were live-trapped and released outside. Deer ≥12 weeks old were able to jump the fence. Four similar plots were established, but without a predator exclusion fence. Fawn and adult female ratios were determined using two camera traps in each plot, for two weeks in August 2011 and two weeks in August 2012.
A study in 1995–2010 on a shrubland-dominated peninsula in Western Australia, Australia (10) found that a translocated population of western barred bandicoots Perameles bougainville did not persist despite fencing to exclude invasive red foxes Vulpes vulpes and cats Felis catus. Nine years after being translocated into a fenced area, bandicoot numbers increased to an estimated 467 but over the next three years, the population fell to zero. Fourteen bandicoots were initially translocated in 1995–1996 from an offshore island to a 17-ha enclosure within a 1,200-ha section of a mainland peninsula, fenced to exclude foxes and feral cats. The peninsular fence was built in 1989 and despite being rebuilt and repaired several times, it was never an effective barrier to foxes and cats. Throughout the study period, foxes and cats were controlled inside the fenced area by baiting (using 1080 poison) and cats were also trapped and shot. Starting in May 1997 and over 10 years, 82 bandicoots were released from the enclosure to the fenced peninsula. Bandicoots were monitored along a 40 km track network, with cage traps set at 100-m intervals over two nights each three months from August 1995-October 2002 and then twice/year until September 2010 (25,000 trap-nights).
(1) Rouco C., Ferreras P., Castro F. & Villafuerte R. (2008) The effect of exclusion of terrestrial predators on short-term survival of translocated European wild rabbits. Wildlife Research, 35, 625–632, https://doi.org/10.1071/wr07151
(2) Winnard A.L. & Coulson G. (2008) Sixteen years of Eastern Barred Bandicoot Perameles gunnii reintroductions in Victoria: a review. Pacific Conservation Biology, 14, 34–53, https://doi.org/10.1071/pc080034
(3) Read J.L. & Cunningham R. (2010) Relative impacts of cattle grazing and feral animals on an Australian arid zone reptile and small mammal assemblage. Austral Ecology, 35, 314–324, https://doi.org/10.1111/j.1442-9993.2009.02040.x
(4) Morris G., Hostetler J.A., Conner L.M. & Oli M.K. (2011) Effects of prescribed fire, supplemental feeding, and mammalian predator exclusion on hispid cotton rat populations. Oecologia, 167, 1005–1016, https://doi.org/10.1007/s00442-011-2053-6
(5) Guerrero-Casado J., Ruiz-Aizpurua L. & Tortosa F. S. (2013) The short-term effect of total predation exclusion on wild rabbit abundance in restocking plots. Acta Theriologica, 58, 415–418, https://doi.org/10.1007/s13364-013-0140-2
(6) Karmacharya B., Hostetler J.A., Conner L.M., Morris G. & Oli M.K. (2013) The influence of mammalian predator exclusion, food supplementation, and prescribed fire on survival of Glaucomys volans. Journal of Mammalogy, 94, 672–682, https://doi.org/10.1644/12-mamm-a-071.1
(7) Matchett M.R., Breck S.W. & Callon J. (2013) Efficacy of electronet fencing for excluding coyotes: a case study for enhancing production of black-footed ferrets. Wildlife Society Bulletin, 37, 893–900, https://doi.org/10.1002/wsb.348
(8) Frank A.S., Johnson C.N., Potts J.M., Fisher A., Lawes M.J., Woinarski J.C., Tuft K., Radford I.J., Gordon I.J., Collis M.A. & Legge S. (2014) Experimental evidence that feral cats cause local extirpation of small mammals in Australia’s tropical savannas. Journal of Applied Ecology, 51, 1486–1493, https://doi.org/10.1111/1365-2664.12323
(9) Conner L.M., Cherry M.J., Rutledge B.T., Killmaster C.H., Morris G. & Smith L.L. (2016) Predator exclusion as a management option for increasing white‐tailed deer recruitment. The Journal of Wildlife Management, 80, 162–170, https://doi.org/10.1002/jwmg.999
(10) Short J. (2016) Predation by feral cats key to the failure of a long-term reintroduction of the western barred bandicoot (Perameles bougainville). Wildlife Research, 43, 38–50, https://doi.org/10.1071/wr15070
Invasive Non-Native/Alien Species/Diseases
9.3. Remove/control non-native amphibians (e.g. cane toads)
https://www.conservationevidence.com/actions/2498
- We found no studies that evaluated the effects on mammals of removing or controlling non-native amphibians.
‘We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Whilst there are relatively few documented examples of non-native amphibians having direct detrimental impacts on native mammals, the spread of cane toads Bufo marinus in Australia is reported to have accelerated declines in northern quoll Dasyurus hallucatus which are poisoned in predation attempts on the toads (Woinarski et al. 2011). A range of methods for controlling cane toads, including biological control, have been proposed (e.g. Shanmuganathan et al. 2010; Ward-Fear et al. 2010).
Shanmuganathan T., Pallister J., Doody S., McCallum H., Robinson T., Sheppard A., Hardy C., Halliday D., Venables D., Voysey R., Strive T., Hinds L. & Hyatt A. (2010) Biological control of the cane toad in Australia: a review. Animal Conservation, 13(S1), 16–23, https://doi.org/10.1111/j.1469-1795.2009.00319.x
Ward-Fear G., Brown G.P. & Shine R. (2010) Using a native predator (the meat ant, Iridomyrmex reburrus) to reduce the abundance of an invasive species (the cane toad, Bufo marinus) in tropical Australia. Journal of Applied Ecology, 47, 273–280, https://doi.org/10.1111/j.1365-2664.2010.01773.x
Woinarski J.C.Z., Legge S., Fitzsimons J.A., Traill B.J., Burbidge A.A., Fisher A., Firth R.S.C., Gordon I.J., Griffiths A.D., Johnson C.N., McKenzie N.L., Palmer C., Radford I., Rankmore B., Ritchie E.G., Ward S. & Ziembicki M. (2011) The disappearing mammal fauna of northern Australia: context, cause, and response. Conservation Letters, 4, 192–201, https://doi.org/10.1111/j.1755-263x.2011.00164.x
9.4. Remove/control non-native invertebrates
https://www.conservationevidence.com/actions/2501
- One study evaluated the effects on mammals of removing or controlling non-native invertebrates. This study was in the USA1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Abundance (1 study): A replicated, controlled, before-and-after study the USA1 found that after the control of red imported fire ants, capture rates of northern pygmy mice increased.
BEHAVIOUR (0 STUDIES)
Background
Non-native invertebrates can affect mammals in a number of ways. Alterations to habitats and predation on other species could reduce feeding resources available to mammals and, in some cases, direct predation on mammals can occur (Masser & Grant 1986). Such effects can lead to mammals avoiding areas occupied by non-native invertebrates (Killion & Grant 1993). Control of such species may be carried out in an attempt to reverse these impacts.
Masser M.P. & Grant W.E. (1986) Fire ant-induced trap mortality of small mammals in east-central Texas. The Southwestern Naturalist, 31, 540–542.
Killion M.J. & Grant W.E. (1993) Scale effects in assessing the impact of imported fire ants on small mammals. The Southwestern Naturalist, 38, 393–396.
A replicated, controlled, before-and-after study in 1989–1990 in coastal grassland and shrubland in Texas, USA (1) found that after the control of red imported fire ants Solenopsis invicta, capture rates of northern pygmy mice Baiomys taylori increased. Northern pygmy mouse capture rates increased more where red fire ants were controlled (from 6–9/plot during first three months (over winter) of ant control to 19–25/plot nine months later) than in uncontrolled areas (8–9/plot during first three months of ant control to 11–15/plot nine months later). Captures were similar between plots in the summer before treatments began (19–27 mice/plot). In June 1989, two 110 × 130-m plots were established at the Welder Wildlife Foundation refuge. Each plot was divided into a treatment area and an untreated area. In treatment areas, an aerosol insecticide (active ingredient 0.7% pyrethrin) was injected directly into ant mounds while a bait insecticide (active ingredient 0.88% amidinohydrazone) was deployed monthly, from November 1989 to October 1990. Between June 1989 and October 1990, mice were sampled for four days/month using 108 baited Sherman live traps/plot. Animals were marked at first capture, and only included in analysis when caught for a second time.
(1) Killion M.J., Grant W.E. & Vinson S.B. (1995) Response of Baiomys taylori to changes in density of imported fire ants. Journal of Mammalogy, 76, 141–147.
9.5. Remove/control non-native mammals
https://www.conservationevidence.com/actions/2504
- Twenty-five studies evaluated the effects on non-controlled mammals of removing or controlling non-native mammals. Twenty-one studies were in Australia1–5,6a–f,7,10a,10b,12–18, and one was in each of France8, the UK9, Equador11 and the USA19.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (24 STUDIES)
- Abundance (21 studies): Ten of 18 controlled, before-and-after or site comparison studies, in Australia1–4,6a–f,7,10a,10b,12,13,14,16,17, found that after controlling red foxes, abundances, densities or trapping frequencies increased for rock-wallaby spp.1,6a,14,16 eastern grey kangaroo3, woylie6b,, brush-tail possum6b,6c,6d,6f,12 tammar wallaby6b,6c,6d,6f, chuditch12 and quenda12. Seven studies found mixed results with increases in some species but not others6e,7,10a,10b,13, increases followed by declines17 or increases only where cats as well as foxes were controlled4. The other study found no increase in bush rat numbers with fox control2. One of three replicated, before-and-after studies (including two controlled studies), in Australia5, France8 and Ecuador11, found that control of invasive rodents increased numbers of lesser white-toothed shrews and greater white-toothed shrews8. One study found that Santiago rice rat abundance declined less with rodent control11 and one found mixed results, with increased numbers of short-tailed mice at one out of four study sites5.
- Survival (1 study): A replicated, controlled study in Australia3 found that controlling red foxes increased survival of juvenile eastern grey kangaroos.
- Occupancy/range (3 studies): Three studies (two before-and-after, one controlled), in the UK9 and Australia15,18, found that after controlling non-native American mink9, red foxes15 and European rabbits18, there were increases in ranges or proportions of sites occupied by water vole9, common brushtail possum, long-nosed potoroo and southern brown bandicoot15 and four native small mammal species18.
BEHAVIOUR (1 STUDY)
- Behaviour change (1 study): A before-and-after study in the USA19 found that following removal of feral cats, vertebrate prey increased as a proportion of the diet of island foxes.
Background
Non-native species are a threat to native fauna worldwide. Among mammals, non-native carnivores, typically transported by early European settlers, are especially a threat through predation of native species, including mammals, in locations with few native carnivore species. Non-native herbivores can have dramatic habitat impacts, and thus alter suitability of locations or food availability for native species. Control of non-native species can be expensive and benefits may be difficult to maintain, except in island situations where total elimination might be achievable. Nonetheless, actions aimed at reducing populations of non-native mammals may be carried out on an ongoing basis for the benefit of native species, including mammals.
See also: Remove/control non-native mammals within a fenced area and Remove or control predators.
A replicated, controlled, before-and-after study in 1979–1990 in four granite outcrop sites in Western Australia, Australia (1) found that after red fox Vulpes vulpes control, numbers of rock wallabies Petrogale lateralis increased. Results were not tested for statistical significance. In the two sites where fox control was carried out, there were more rock-wallabies after eight years of fox control (50–116 wallabies) than prior to fox control (10–29 wallabies). Over the same period, in the two sites where there was no fox control, wallaby populations declined (after: 0–13; before 7–32). Foxes were initially controlled by shooting and, later, by baiting with fowl eggs dosed with 4.5 mg of 1080 poison. Baiting occurred during the dry seasons of 1980–1983. In 1986–1990, baits were laid along tracks every four to five weeks. Rock-wallabie numbers were estimated by the frequency of recaptures in 1979, 1986 and 1990.
A controlled, before-and-after study in 1993–1995 in four mountain forest sites in the Australian Capital Territory, Australia (2) found that after baiting with poison to control invasive red foxes Vulpes vulpes, bush rat Rattus fuscipes numbers did not increase. Bush rat numbers at the end of the study were higher in sites with fox control (11–14 animals) compared to without (6–8 animals). However, in sites with control, bush rat numbers were similar 22 months after fox control began (11–14 animals) compared to immediately beforehand (11–12 animals; results not statistically tested). Four 10–28 km2 sites were studied in Namadgi National Park. Fox control started in two sites in July 1993 using 1080 poison bait, and in two sites there was no fox control. Red fox numbers in baited sites were reduced from 2.8–3.4/km to <0.5/km in six months and to almost zero over the following 12 months, while fox density remained stable and approximately five times higher in unbaited sites. Bush rats were monitored on two plots in unbaited sites (>2 km apart) and in one plot in baited sites. In total, two trap lines (25 m apart) of 15 Elliott live traps were set at 10–14 m intervals for three consecutive nights, every two months from June 1993 to March 1995 (6,480 trap nights). Foxes were surveyed using spotlights along transects.
A replicated, controlled study in 1993–1995 in four open grassy sites in the Australian Capital Territory, Australia (3) found that controlling invasive red foxes Vulpes vulpes increased eastern grey kangaroo Macropus giganteus population growth rates and juvenile survival. Kangaroo population growth rates were higher in fox control sites than in uncontrolled sites (data reported as statistical model outputs). In sites with fox control the proportion of females with pouch young was similar at the end of pouch emergence (0.87–0.88 females with young) compared to at the beginning (0.78–0.80 females with young), whereas in sites without fox control, the proportion of females with young declined by 50% by the end of the pouch emergence phase (0.55–0.61 females with young) compared to the beginning (0.94–0.97 females with young). Foxes were removed from two sites within Namadgi National Park using 35 g FOXOFF baits (containing 0.3 mg of 1080 poison). Baiting commenced in July 1993 and reduced fox numbers from 2.8–3.4/km to <0.5/km within six months and to almost zero over the following 12 months. Fox numbers in two unbaited sites remained relatively constant (0.8–2/km). Kangaroos were counted in four sites (two with fox control and two without) 1 hour before dusk from a slow moving car (<5 km/h) along 1.5–2 km transects (400–700 m wide). Surveys were conducted in August, October and December 1993 and then monthly until March 1995. Transects were surveyed twice each survey period.
A before-and-after, controlled study in 1990–1994 in three sites in Western Australia, Australia (4) found that where both cats Felis catus and foxes Vulpes vulpes were controlled, captures of small mammals increased but where only foxes were controlled, they decreased. Combined fox and cat control doubled small mammal abundances (after: 93; before: 42 individuals captured), but counts fell by 80% where only foxes were controlled (after: 7; before: 55 individuals captured). Small mammal abundances remained similar where no predators were controlled. See original paper for full results. In 1991, a mainland peninsula was divided in three areas in which 1) both cats and foxes were controlled by using an electrified fence, poison baiting (dried meat or cat food with 4.5 mg 1080 poison or via secondary poisoning by poisoning rabbits Oryctolagus cuniculus), and trapping or shooting (12 km2), 2) foxes were controlled by baiting (120–200 km2) but cats were not targeted or 3) no control occurred. Predators were surveyed over 3–4 nights in vehicles using spotlights (transect length: 7.5–20 km). Small mammals were monitored with six pitfall-trap grids in each area. Each grid had eight pitfall traps, 30–50 m apart. Sampling was conducted over three consecutive days in March–April and June–July in 1990–1994 in predator control areas and 1992–1994 in the area without predator control.
A replicated, controlled, before-and-after study in 1999 at six shrub and grassland sites on an island in Western Australia, Australia (5) found that baiting to control invasive house mice Mus domesticus increased the density of short-tailed mice Leggadina lakedownensis in one out of four comparisons. Twenty-two days after baiting, the minimum abundance of short-tailed mice was higher in one site with bait deployed every 10 m than before baiting (12.7 vs 7.0 mice). Short-tailed mouse numbers were low in all other sites (baited and unbaited) and were similar after baiting compared to before (see original paper for details). House mice numbers declined on all baited sites (pre-baiting: 5.8–6.2 mice/ha; post baiting: 2.5–2.7 mice/ha). Six grids were established in individual sites at least 1 km apart in May 1999. Two sites were baited with ‘Talon’ (15-g wax blocks containing 0.005% brodifacoum) at 10 m intervals (117 bait stations/grid), two were baited at 20 m intervals (45 bait stations/grid) and two were unbaited. Bait was replenished every two days for seven days and then again on the fourteenth day. Each site had 25 trap stations arranged in a 5 x 5 pattern, each with one pitfall trap and associated 5 m drift-fencing and one Elliott trap. Sites were monitored for two nights before baiting and up to 22 nights after baiting.
A before-and-after, site comparison study in 1979–1990 on two islands in Western Australia, Australia (6a) found that following control of red foxes Vulpes vulpes using poisoned baits, numbers of Rothschild’s rock wallaby Petrogale rothschildi increased. Results were not tested for statistical significance. After six years of fox control, wallaby numbers were higher (8.8 sightings/hour) than before control (0.3 sightings/hour). During the same period, numbers remained stable on a nearby fox free island (before: 18.7; after: 19.2 sightings/hour). Foxes were controlled by baiting on Dolphin island (3,203 ha), Dampier Archipelago. Meat baits or intact fowl eggs, laced with 1080-poison, were deployed manually in limited areas in October 1980 and May 1981 and then deployed aerially on a larger scale, three times from September 1984 to October 1989. Foxes were also controlled on neighbouring islands and the nearby mainland to prevent immigration (see original paper for details). In 1979–1980 and in 1990, spotlight counts of rock-wallabies were carried out on both Dolphin Island and the nearby fox-free Enderby Island (3,290 ha). Surveys were conducted on foot using a long range 100-W spotlight (1979–1980: 10; 1990: 4 hours of surveying). No fox abundance data are provided.
A before-and-after study in 1979–1998 in a forest reserve in Western Australia, Australia (6b) found that after baiting with poison to control red foxes Vulpes vulpes, numbers of woylies Bettongia penicillata, brush-tail possums Trichosurus vulpecula and tammar wallabies Macropus eugenii increased. Results were not tested for statistical significance. After eight years of fox control, numbers were higher than before control for woylies (after: 1.3; before: 0.0 sightings/hour, after: 0.2–0.3; before: 0.0 individuals/trap night), brush-tail possums (after: 7.7; before: 0.4 sightings/hour) and tammar wallabies (after: 9.4; before: 0.4 sightings/hour). Numbers of tammar wallabies continued to increase up to 14 years after the start of fox control (40 sightings/hour). Foxes were controlled by baiting from 1984 in Tutanning Nature Reserve (2,200 ha). Baits (1080-poison meat baits or intact fowl eggs) were deployed monthly. Mammals were surveyed in 1979–1998 by repeated spotlight counts along 50 circuits near to the boundary of the reserve (circuit length is not provided). Woylies were also monitored using cage traps at 100 m intervals on 1 km-long transects (380 trap nights in 1979; 322 trap nights in 1984; 320 trap nights in 1989; 266 trap nights in 1992). Spotlight searches were conducted using long range 100-W lights.
A before-and-after study in 1987–1998 in a forest reserve in Western Australia, Australia (6c) found that after baiting with poison to control red foxes Vulpes vulpes, numbers of brush-tail possums Trichosurus vulpecula and tammar wallabies Macropus eugenii increased. Results were not tested for statistical significance. Three years after the start of fox control, numbers of tammar wallaby (105.2 sightings/hour) and brush-tail possums (10.5 sightings/hour) increased compared to prior to fox control (wallabies: 4.8 sightings/hour; brush-tail possums: 0 sightings/hour). Numbers of tammar wallabies (61.7 sightings/hour) and brush-tail possums (6.3 sightings/hour) remained higher nine years after fox control started. Foxes were controlled using poison baits (1080-poison meat baits or intact fowl eggs) from 1989 in a separate annex of Tutanning Nature Reserve (114 ha). Mammals were surveyed in 1987, 1992 and 1998 by repeated spotlight counts using long range 100 W lights.
A before-and-after, site comparison study in 1985–1996 in a forest reserve in Western Australia, Australia (6d) found that after baiting with poison to control red foxes Vulpes vulpes, numbers of brush-tail possums Trichosurus vulpecula and tammar wallabies Macropus eugenii increased and translocated woylies Bettongia penicillata were still present. Results were not tested for statistical significance. Numbers of brush-tail possums and tammar wallabies were higher in an area where foxes had been baited for seven years than in an area baited for three years (brush-tail possums: 9.1 vs 0.3; tammar wallabies: 1.8 vs 0.0). Four years after translocation, woylies, which were absent prior to fox control, were found to number eight individuals on the east side and 59 on the west side. Foxes were controlled by baiting from 1985 in the east area of the Boyagin Nature Reserve (4,780 ha) and from 1989 in the west. Baits (1080-poison meat baits or intact fowl eggs) were deployed monthly. Mammals were surveyed in 1989–1992 by repeated spotlight counts using long range 100-W lights and cage traps at 100 m intervals on 1 km-long transects in 1992 and 1996 (150 trap nights/area). In total 40 woylies were translocated in 1992 (20 released in the east and 20 in the west area).
A before-and-after study in 1970–1992 in a forest reserve in Western Australia, Australia (6e) found that after baiting with poison to control red foxes Vulpes vulpes, numbers of woylies Bettongia penicillata and brush-tail possums Trichosurus vulpecula increased, but tammar wallabies Macropus eugenii numbers did not. Results were not tested for statistical significance. Three years after the start of widespread fox control, overall numbers of individuals were higher than before control for woylies (after: 27.7; before: 1.2 sightings/hour) and brush-tail possums (after: 22.3; before: 2.8 sightings/hour) but tammar wallaby sightings remained infrequent (0 sightings/hour). Ten years after baiting began in a restricted area where fox control was tested before widespread control commenced, numbers of individuals were higher than before control for woylies (after: 23; before: 0.4 sightings/hour), brush-tail possums (after: 9.9; before 2.0 sightings/hour) and tammar wallabies (after: 1.23; before: 0.5 sightings/hour). Foxes were controlled by baiting in a restricted area from 1982, and across the whole reserve from 1989 in a 12,000 ha forest fragment in Dryandra Woodlands. Baits (1080-poison meat baits or intact fowl eggs) were deployed monthly. Mammals were surveyed before fox control in 1970–1971 (75 hours), once the restricted area baiting trial had commenced in 1987 (5 hours) and 1989 (8 hours), and after baiting had been extended to the whole reserve in 1990 (4.5 hours) and 1992 (5.7 hours). Repeated spotlight surveys were conducted along 49 routes using long range 100-W lights (route length is not provided). Woylies were also trapped in cages (see original paper for details).
A site comparison study in 1991–1998 in a national park in Western Australia, Australia (6f) found that after baiting with poison to control red fox Vulpes vulpes, numbers of brush-tail possums Trichosurus vulpecula and tammar wallabies Macropus eugenii increased. Results were not tested for statistical significance. Four years after the start of fox control, brush-tail possum and wallaby numbers were higher in areas where foxes were controlled than in areas where they were not (possums: 19.3 vs 1.1 sightings/hour; wallabies: 5.47 vs 0.0 sightings/hour). Trapping success rates for brush-tail possums were higher in baited compared to unbaited areas and increased every year in fox control areas (see original paper for details). Foxes were controlled in half of the 329,000-ha Fitzgerald River National Park. The other half of the park was left unbaited. Baits (dried meat with 4.5 mg of 1080 poison) were distributed aerially twice a year in 1991–1995 at a density of six baits/km2. Supplementary bait was also distributed in some areas by vehicle in 1995–1996. Mammals were surveyed by repeated spotlight surveys using long range 100-W lights (unbaited area: 9.4 hours in 1994–1995; baited area: 17.1 hours in 1993–1996) and trapping (possums only) in 1994–1998 (4 km long trap lines with 40 traps set at 100 m intervals).
A replicated, site comparison study (year not stated) in eight swamp shrubland sites in Western Australia, Australia (7) found that controlling non-native red foxes Vulpes vulpes had mixed effects on quokka Setonix brachyurus populations. Results were not tested for statistical significance. In 10 of 15 comparisons, sites where foxes were controlled had higher quokka densities than did areas where foxes were not controlled (0.1–4.3 vs 0 quokkas/ha). In five of 15 comparisons, there were fewer or equal numbers of quokkas in fox-control and uncontrolled sites (0–0.07 vs 0–1.1 quokkas/ha). Starting in an unspecified year, once a month, at five sites, meat laced with 1080 poison was laid at 100-m intervals. At three sites, no bait was laid. Five baits/km2 were also dropped from aircraft in the area surrounding baited sites. In each site two wire cage traps were placed every 50–100 m along a stream. One trap, measuring 0.90 × 0.45 × 0.45 m, was baited with apples. The other trap, measuring 0.59 × 0.205 × 0.205 m, was baited with peanut butter, rolled oats, honey, and pilchards. Quokkas were caught and released over an eight-day period at each site and were fitted with transponder microchips to allow individual identification.
A replicated, before-and-after study in 1994–2004 on five temperate oceanic islands in northern France (8) found that after the eradication of Norway rats Rattus norvegicus, the abundance of lesser white-toothed shrews Crocidura suaveolens increased on four islands and greater white-toothed shrews Crocidura russula increased on one island. No statistical analyses were performed. Ten years after rat eradication, the abundance of lesser white-toothed shrews on four islands was greater than that before rat eradication (after: 0.09–0.14 shrews/trap night; before: 0.00–0.01). One and two years after rat eradication on a further island, the abundance of greater white-toothed shrews was greater than that before rat eradication (after: 0.31 shrews/trap night; before: 0.02). In total, Norway rats were eradicated from seven islands (0.2–21 ha) in 1994–2002 by trapping and baiting with anticoagulant rodenticide (Bromadiolone©) or using strychnine poisoning (one island in 1951). Monitoring results from five islands are reported here. Small mammal sampling was conducted with 7–269 trap stations at 6–30 m intervals in 1994–2004. Each station had two live traps and was checked daily for 3–7 days.
A before-and-after study in 1997–2005 along a river in Norfolk, UK (9) found that after controlling invasive American mink Mustela vison, the proportion of sites occupied by water voles Arvicola terrestris increased. Results were not tested for statistical significance. After two years of mink control, a higher proportion of sites were occupied by water voles (27 of 59 sites, 46%) than before control (21 of 62 sites, 35%). No mink signs were found at any survey sites in 2005. Over 280 mink were trapped and euthanised along the River Wensum and its tributaries using traps on banks (1.3–1.6 mink/traps over 3 years, 262 individual mink) and rafts (1.8–2.2 mink/raft over 2 years, 18 individual mink). Between 200 and 220 bank traps (in 2004–2006) and 5–10 raft traps (in 2004–2005) were deployed. Raft traps were arranged in clusters of two to four with clusters at 1–5 km intervals. Water voles were surveyed in 1997 (62 sites), 2003 (60 sites) and 2005 (59 sites) by searching for water vole signs (e.g. latrines, burrows) along 500 m sections of waterway.
A before-and-after study in 1995–2002 in heath and forest habitats in New South Wales, Australia (10a) found that after controlling invasive red foxes Vulpes vulpes, one of seven mammal species increased. After four years of fox control, more common ringtail possums Pseudocheirus peregrinus were detected than before control (after: 1.8; before: 0.7 individuals/100 m). However, numbers remained similar between fox control and pre-control periods for long-nosed bandicoots Perameles nasuta (1.5 vs 0/transect), bush rats Rattus fuscipes (1.5 vs 0/transect), brown antechinus Antechinus stuartii (3.8–7.6 vs 3.2–3.6/transect), sugar gliders Petaurus breviceps (0.1–0.3 vs 0.1–0.2/100 m), black rats Rattus rattus (0.9–3.9 vs 2.6–5.8/transect) and common brushtail possum Trichosurus vulpecula (0.1–0.3 vs 0.0–0.1/100 m). Control, initiated in 1996, was performed over two weeks, in March and August, using FOXOFF® baits containing 3 mg of 1080 poison. Baits were placed 300–900 m apart. Terrestrial mammals were surveyed two years prior to fox control starting (1995–1996) and up to six years afterwards (in 1999, 2000, 2002). Trapping was over four nights between January and March, along five transects, using 20–25 Elliott live traps/transect and 3–4 possum traps/transect, set 20 m apart. Arboreal mammals were surveyed one year prior to fox control starting (1995) and up to 6 years afterwards (in 1996, 1999, 2000, 2002), along five 500-m-long spotlight transects, 1–2 hours after dark.
A site comparison study in 1999–2003 in New South Wales, Australia (10b) found that controlling invasive red foxes Vulpes vulpes increased abundances of four out of five small mammal species. After four years of fox control, numbers of brown antechinus Antechinus stuartii, bush rat Rattus fuscipes, black rat Rattus rattus and long-nosed bandicoot Perameles nasuta, but not of common brushtail possum Trichosurus vulpecula, were higher than in a site where foxes were not controlled (antechinus: 35 vs 17; bush rat: 29 vs 1; black rat: 1 vs 0; bandicoot: 3 vs 0; possum: 0 vs 4; results not tested for statistical significance). At Booderee National Park, fox control was conducted twice a year between 1999 and 2003 in March and August, using 3 mg 1080 FOXOFF® poison baits, 300–1,000 m apart. No control occurred at Jervis Bay National Park. In both parks, mammals were surveyed over five days in May 2003, along eight 120 m transects, using six Elliott live traps, three possum cage traps and three wire bandicoot traps, spaced 10 m apart. Transects were located at least 500 m apart.
A randomized, replicated, controlled, before-and-after study in 2002–2003 in arid shrubland on an island in Ecuador (11) found that control of invasive black rats Rattus rattus reduced the rate of seasonal declines in the abundance of Santiago rice rats Nesoryzomys swarthi. Rice rat abundance declined in all sites regardless of black rat control (with control: from 11 to 8–9; without control: from 18–19 to 11–12 rats), but the rate of decline was slower in sites where black rats were controlled (data presented as statistical model outputs). The rate of immigrating female rice rats was higher where black rats were controlled (data presented as statistical model outputs). Black rat numbers decreased more in sites with black rat control (from 18 to 1 rat) compared to sites without black rat control (from 14 to 3 rats). Three sites were selected in Santiago Island, Galapagos. In each site, two trapping grids were set up (98 traps set in pairs at 30 m intervals), in one grid all black rats caught were euthanised and in the other black rats were released after capture. Six trapping sessions were carried out between December 2002 and September 2003 in which each site was trapped for five nights. Additional trapping was conducted 8–10 days after the normal trapping to remove ‘immigrant’ black rats. Supplementary food (5 kg of rolled oats, 750 ml of vegetable oil and 600 g of peanut butter) was distributed in each site every six days.
A before-and-after study in 1980–2005 across an area of former bauxite mines in jarrah forest of Western Australia, Australia (12) found that controlling non-native red foxes Vulpes vulpes on restored mine areas resulted in increased abundance of chuditch Dasyurus geoffroii, quenda Isoodon obesulus and brushtail possum Trichosurus vulpecula. Results were not tested for statistical significance. Chuditch were caught in 0.2% of traps immediately after fox removal compared to none before, and in 1.4% of traps six years later. Quenda were caught in 2.7% of traps immediately after fox removal compared to none before, but they were also absent six years after fox removal. Brushtail possum were caught in 2.3% of traps six years after fox removal, compared to up to 0.5% before. Control of foxes, using poisoned baits, was carried out from 1994 and fox sightings decreased from 15 that year to none in 1999 and 2000. Mined areas were revegetated using various techniques. Mammals were monitored using wire cage traps, large and medium aluminium box traps and pit traps in 1980, 1993, 1997 and 2005.
A replicated, paired sites, controlled, before-and-after study in 1997–2003 in six forest sites in Australia (13) found that controlling invasive red foxes Vulpes vulpes increased overall native mammal abundance and abundances of three out of five species. The average number of trapped mammals was higher in fox-control (11.0) than in non-control sites (5.2). Average numbers of individuals trapped/session were higher in fox-control than in non-control sites for long-nosed potoroos Potorous tridactylus (5.1 vs 2.3), southern brown bandicoots Isoodon obesulus (2.3 vs 1.2) and common brushtail possums Trichosurus vulpecula (3.1 vs 1.0), but not for ringtail possums Pseudocheirus peregrinus or long-nosed bandicoots Perameles nasuta (numbers not given). Increases in abundance over time were found for long-nosed potoroos and ringtail possums, but not for southern brown bandicoots, common brushtail possums or long-nosed bandicoot (results from statistical models). In 1999–2003, foxes were controlled in three out of six forest sites (7,000–16,500 ha) and no control was conducted in the remaining three sites. From February 1999, baits (Foxoff Econbaits, containing 3 mg of 1080 poison) were buried at 15 cm depth every four weeks, at 1-km intervals. At each site, native mammals were surveyed over seven nights, along an 18-km transect, using 60 baited traps, set at 300-m intervals. Trapping was conducted twice before fox-control started (1997–1998) and 12 times after control started (July 1999–May 2003).
A replicated, before-and-after study in 1979–2007 at four sites in Western Australia, Australia (14) found that controlling non-native red foxes Vulpes vulpes resulted in an increase in the number of rock wallabies Petrogale spp. At all four sites, 10–24 years after fox control began, rock wallaby populations were higher (33–300 animals), than before fox control began (1–32 animals). Starting in 1982, baits containing 1080 poison were laid monthly around four wildlife reserves. At each site, where there were signs of rock wallabies, 30 live traps were baited with apples over a three-day period. Traps were set each evening and checked at dawn, in December–April and February–March of 1979–2007. All rock wallabies caught were tagged, weighed, and released near their capture site.
A replicated, controlled study in 2005–2013 in six forest areas in Australia (15) found that after using poison bait to control invasive red foxes Vulpes vulpes, occupancy rates of common brushtail possum Trichosurus vulpecula, long-nosed potoroo Potorous tridactylus and southern brown bandicoot Isoodon obesulus increased. The number of sites occupied by common brushtail possum (51), long-nosed potoroo (20) and southern brown bandicoot (25) was higher in areas where foxes were controlled than in other areas (common brushtail possum: 44; long-nosed potoroo: 7; southern brown bandicoot: 13). Six areas with no previous fox control where selected. From October 2005–November 2013, foxes were baited in three areas (4,703–9,750 ha) using FoxOff® (containing 3 mg of 1080 poison). Every 1 km, one bait was buried at a depth of 10 cm and replaced fortnightly. Three other areas (4,659–8,520 ha) were left unbaited. In each of the six areas, mammals were monitored annually at 40 sampling sites using hair tubes. Tubes were set for four days in spring 2005 and 2008–2013 and winter 2006 and 2007, and species were identified from hairs.
A replicated, controlled, before-and-after study in 1980–2012 in four mixed eucalyptus woodland and shrubland in southern Australia (16) found that after control of invasive red foxes Vulpes vulpes, population growth rates of yellow-footed rock wallabies Petrogale xanthopus increased. In the two populations exposed to fox control, rock-wallaby population growth rates were higher after fox control commenced than before (data presented as statistical model outputs). Over the same time periods, rock-wallaby population growth rates were similar in colonies where foxes were not controlled (data presented as statistical model outputs). In New South Wales, the number of rock-wallabies counted increased two years after fox control began (at start of fox control: 7; after: 16 animals), while in the site without fox control numbers remained similar. Two sites in New South Wales and two in South Australia were studied. In each state, foxes were controlled in one site and not controlled in the other site. Baiting strategy differed by location (see original paper for details). Bait stations (219 in New South Wales and 100 in South Australia) were baited using Foxoff Econobaits® or fresh or dried meat laced with 1080 poison. Baits were deployed from June 1995 in New South Wales and from June 2004 in South Australia. Wallabies were surveyed annually, over three mornings in the winter months, from a helicopter. Surveys were conducted in 1980–2001 (New South Wales) and 2000–2012 (South Australia).
A replicated, before-and-after study in 1970–2009 in two forest sites in Western Australia, Australia (17) found that controlling invasive red foxes Vulpes vulpes initially increased the abundance of woylies Bettongia penicillata, but woylie numbers returned to pre-control levels after about 25 years. Results were not tested for statistical significance. After 25 years of fox control, the trapping success of woylies (caught in 3–8% of traps from 2002–2006) was only marginally higher than pre-control levels (2–3% from 1970–1975). However, trapping success had increased up to 28–65% during the first 20 years after the start of fox control. Between April 2006 and October 2009, more woylies were killed by cats Felis catus (65%) than by foxes (21%). Foxes were controlled from the mid-1970s at two reserves (2–6,800 ha) by baiting (either dry meat with 3 mg of 1080 poison or Pro-baits) with 5 baits/km2 every four weeks. No details about long-term woylie trapping are provided. Between April 2006 and October 2009, 146 woylies were radio-collared, of which 89 died. Cause of death was determined by DNA analysis and predation characteristics.
A before-and-after study in 1970–2014 in an arid region in South Australia, Australia (18) found that control of invasive European rabbits Oryctolagus cuniculus, using rabbit hemorrhagic disease virus, increased the area occupied by four native small mammal species. The extent of occurrence and area of occupancy (both expressed in thousands of km2) was greater after outbreaks of rabbit hemorrhagic disease than before for spinifex hopping mouse Notomys alexis (extent: 276–356 vs 180; area: 7–8 vs 3), dusky hopping mouse Notomys fuscus (extent: 105–130 vs 23; area: 6–11 vs 2), plains mouse Pseudomys australis (extent: 217–252 vs 63; area: 4–6 vs 2) and crest-tailed mulgara Dasycercus cristicauda (extent: 98–133 vs 1; area: 12–13 vs 1). After the first virus outbreak, rabbit abundance decreased by 85% (raw data not provided) in one site and from 139 to 22 rabbits/km2 in the other site. Cat Felis catus and fox Vulpes vulpes numbers followed rabbit population trends. Occurrence records over a 615,000 km2 region were compiled from published sources and divided into periods covering before the outbreak (1970–1995) and after first and second outbreaks (1996–2009 and 2010–2014). Area of occupancy was calculated from occupied 10 × 10 km grid squares. Extent of occurrence was calculated from minimum convex polygons around species records. Rabbit abundance was monitored in two long-term study sites using spotlight transects.
A before-and-after study in 2006–2012 of scrubland on an island in California, USA (19) found that following removal of feral cats Felis catus, vertebrate prey increased as a proportion of the diet of island foxes Urocyon littoralis. The frequency of deer mice Peromyscus maniculatus in fox scats was higher after cat removal (40%) than before (11%). The same pattern held for birds (after: 12% of scats; before: 6% of scats). Lizard frequency in fox scats was not significantly higher after cat removal (10%) than before (5%) and there were not significant changes in frequencies of arthropods, snails or fruit. Authors indicated that increased deer mouse and bird frequency suggests that foxes and cats had been competing for prey. However, fox abundance was more linked to precipitation levels, and declined over the study period. On a 5,896-ha island, feral cats were eradicated in 2009–2010. Fox scats collected before cat removal (1,180 scats, autumn 2006–summer 2009) and after removal (508 scats, autumn 2010–summer 2012) were analysed for food remains.
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(4) Risbey D.A., Calver M.C., Short J., Bradley J.S. & Wright I.W. (2000) The impact of cats and foxes on the small vertebrate fauna of Heirisson Prong, Western Australia. II. A field experiment. Wildlife Research, 27, 223–235, https://doi.org/10.1071/wr98092
(5) Moro D. (2001) Evaluation and cost-benefits of controlling house mice (Mus domesticus) on islands: an example from Thevenard Island, Western Australia. Biological Conservation, 99, 355–364, https://doi.org/10.1016/s0006-3207(00)00231-7
(6) Kinnear J.E., Sumner N.R. & Onus M.L. (2002) The red fox in Australia—an exotic predator turned biocontrol agent. Biological Conservation, 108, 335–359, https://doi.org/10.1016/s0006-3207(02)00116-7
(7) Hayward M.W., Paul J., Dillon M.J. & Fox B.J. (2003) Local population structure of a naturally occurring metapopulation of the quokka (Setonix brachyurus Macropodidae: Marsupialia). Biological Conservation, 110, 343–355, https://doi.org/10.1016/s0006-3207(02)00240-9
(8) Pascal M., Siorat F., Lorvelec O., Yésou P. & Simberloff D. (2005) A pleasing consequence of Norway rat eradication: two shrew species recover. Diversity and Distributions, 11, 193–198, https://doi.org/10.1111/j.1366-9516.2005.00137.x
(9) Thompson H. (2006) The use of floating rafts to detect and trap American mink Mustela vison for the conservation of water voles Arvicola terrestris along the River Wensum in Norfolk, England. Conservation Evidence, 3, 114–116
(10) Dexter N., Meek P., Moore S., Hudson M. & Richardson H. (2007) Population responses of small and medium sized mammals to fox control at Jervis Bay, Southeastern Australia. Pacific Conservation Biology, 13, 283–292, https://doi.org/10.1071/pc070283
(11) Harris D.B. & Macdonald D.W. (2007) Interference competition between introduced black rats and endemic Galapagos rice rats. Ecology, 88, 2330–2344, https://doi.org/10.1890/06-1701.1
(12) Nichols O.G. & Grant C.D. (2007) Vertebrate fauna recolonization of restored bauxite mines–key findings from almost 30 years of monitoring and research. Restoration Ecology, 15, S116–S126, https://doi.org/10.1111/j.1526-100x.2007.00299.x
(13) Dexter N. & Murray A. (2009) The impact of fox control on the relative abundance of forest mammals in East Gippsland, Victoria. Wildlife Research, 36, 252–261, https://doi.org/10.1071/wr08135
(14) Kinnear J.E., Krebs C.J., Pentland C., Orell P., Holme C. & Karvinen R. (2010) Predator-baiting experiments for the conservation of rock-wallabies in Western Australia: a 25-year review with recent advances. Wildlife Research, 37, 57–67, https://doi.org/10.1071/wr09046
(15) Robley A., Gormley A.M., Forsyth D.M. & Triggs B. (2014) Long-term and large-scale control of the introduced red fox increases native mammal occupancy in Australian forests. Biological Conservation, 180, 262–269, https://doi.org/10.1016/j.biocon.2014.10.017
(16) Sharp A., Norton M., Havelberg C., Cliff W. & Marks A. (2014) Population recovery of the yellow-footed rock-wallaby following fox control in New South Wales and South Australia. Wildlife Research, 41, 560–570, https://doi.org/10.1071/wr14151
(17) Marlow N.J., Thomas N.D., Williams A.A., Macmahon B., Lawson J., Hitchen Y., Angus J. & Berry O. (2015) Cats (Felis catus) are more abundant and are the dominant predator of woylies (Bettongia penicillata) after sustained fox (Vulpes vulpes) control. Australian Journal of Zoology, 63, 18–27, https://doi.org/10.1071/zo14024
(18) Pedler R.D., Brandle R., Read J.L., Southgate R., Bird P. & Moseby K.E. (2016) Rabbit biocontrol and landscape‐scale recovery of threatened desert mammals. Conservation Biology, 30, 774–782, https://doi.org/10.1111/cobi.12684
(19) Cypher B.L., Kelly E.C., Ferrara F.J., Drost C.A., Westall T.L. & Hudgens B.R. (2017) Diet patterns of island foxes on San Nicolas Island relative to feral cat removal. Pacific Conservation Biology, 23, 180–188, https://doi.org/10.1071/pc16037
9.6. Remove/control non-native mammals within a fenced area
https://www.conservationevidence.com/actions/2528
- One study evaluated the effects on native mammals of removing or controlling non-native mammals within a fenced area. This study was in Australia1.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): A site comparison study in Australia1 found that in a fenced area where invasive cats, red foxes and European rabbits were removed, native mammal species richness was higher than outside the fenced area.
POPULATION RESPONSE (1 STUDY)
- Abundance (1 study): A site comparison study in Australia1 found that in a fenced area where invasive cats, red foxes and European rabbits were removed, native mammals overall and two out of four small mammal species were more abundant than outside the fenced area.
BEHAVIOUR (0 STUDIES)
Background
Control of non-native mammals may be carried out to reverse detrimental impacts of such species on native plants and animals. Total elimination of non-native mammals may be difficult or impossible to carry out on a large scale, with control programmes often being confined to small islands, where elimination may be achievable. However, away from islands, a similar benefit might be realised if non-native mammals can be removed from within an area that is fenced to prevent their recolonization.
A site comparison study in 1997–2005 in a dune and shrubland site in South Australia, Australia (1) found that in a fenced area where invasive cats Felis catus, red foxes Vulpes vulpes and European rabbits Oryctolagus cuniculus were removed, native mammal species richness and abundance, and abundance of two out of four small mammal species were greater than outside the fenced area. Two to six years after the removal of cats, foxes and rabbits began, native mammal species richness and overall abundance was higher inside than outside the fenced removal area (data presented on log scales). Also, more spinifex hopping mice Notomys alexis and Bolam’s mice Pseudomys bolami were caught in removal areas (spinifex: 13–51; Bolam’s: 5–38) than in non-removal areas (spinifex: 3–4; Bolam’s: 1–2). Numbers caught did not significantly differ in removal vs non-removal areas for fat-tailed dunnart Sminthopsis crassicaudata (0.3 vs 0.8) and stripe-faced dunnart Sminthopsis macroura (0.3–2.8 vs 1.1). Between 1997 and 2005, a 78-km2 exclosure was established in five stages, inside which rabbits, cats and foxes were removed from 1999. Locally extinct mammals were reintroduced into the first area (14-km2) in 1999–2001. Twelve locations inside the exclosure and 12 outside (60–7,000-km apart) were sampled over four nights annually, in 1998–2005, using a line of six pitfall traps and 15 Elliott live traps.
(1) Moseby K.E., Hill B.M. & Read J.L. (2009) Arid Recovery–A comparison of reptile and small mammal populations inside and outside a large rabbit, cat and fox‐proof exclosure in arid South Australia. Austral Ecology, 34, 156–169, https://doi.org/10.1111/j.1442-9993.2008.01916.x
9.7. Remove/control non-native plants
https://www.conservationevidence.com/actions/2529
- Two studies evaluated the effects on mammals of removing or controlling non-native invasive plants. Both studies were in the USA1,2.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): A replicated study in the USA2 found that control of introduced saltcedar did not change small mammal species richness.
POPULATION RESPONSE (1 STUDY)
- Abundance (1 study): A site comparison study in the USA1 found that partial removal of velvet mesquite did not increase abundances of six mammal species.
BEHAVIOUR (0 STUDIES)
Background
Invasive plants can out compete established plant species and alter habitat structure. This may alter resource availability for mammals. Some mammal species may benefit but, for others, invasive plants may reduce available food or shelter or change the nature of the environment such that they are at increased risk of predation. Removal or control of non-native invasive plants may be carried out in an attempt to reverse these effects.
A site comparison study in 1976–1978 in three desert sites in Arizona, USA (1) found that partial removal of velvet mesquite Prosopis juliflora var. velutina did not increase abundances of six mammal species, and complete removal reduced the abundance of two species. The abundance of black-tailed jackrabbits Lepus californicus was higher in the undisturbed (0.37/km) and partially cleared mesquite sites (0.36/km) than in the cleared, mesquite-free, site (0.06/km). The same pattern held for antelope jackrabbit Lepus alleni (0.37 and 0.56 vs 0.09/km). However, abundances were similar in the undisturbed, partially and fully cleared sites for desert mule deer Odocoileus hemionus crooki (0.30, 0.24 and 0.16/km), javelina Dicotyles tajacu (0.24, 0.15 and 0.00/km), coyote Canis latrans (0.05, 0.06 and 0.01/km) and desert cottontail Sylvilagus audubonii (0.04, 0.02 and 0.03/km). Mesquite was cleared from one 300 ha site in 1955 using diesel oil, and partially removed from a second 300 ha site by clearing seven 2.8–30.4 ha patches by chaining in July 1976. At the third 300 ha site, mesquite was left undisturbed. Mammals were counted monthly along four 1,200-m transects between September 1976 and June 1978.
A replicated study in 2001–2012 in three sites in Nevada, USA (2) found that control of introduced saltcedar Tamarix ramosissima, did not change small mammal species richness. Ten years after saltcedar control commenced, small mammal species richness (3–6 species) was similar to that when control started (3–7 species). Small mammals were trapped annually in May or June for three consecutive nights between 2001 and 2011–2012 at three sites along waterways. An additional trapping period of three nights was conducted in July or August 2001–2004 at one site, and 2001–2006 at two sites. Each night at each site, 2–4 parallel rows of 25 Sherman® live traps, baited with wild birdseed mix, were set with 10 m between traps and 25–100 m between rows. Saltcedar was controlled by leaf beetles Diorhabda spp. released at the sites in 2001–2002.
(1) Germano D.J., Hungerford R. & Martin S.C. (1983) Responses of selected wildlife species to the removal of mesquite from desert grassland. Journal of Range Management, 36, 309–311.
(2) Longland W.S. (2014) Biological control of saltcedar (Tamarix spp.) by saltcedar leaf beetles (Diorhabda spp.): effects on small mammals. Western North American Naturalist, 74, 378–385, https://doi.org/10.3398/064.074.0403
9.8. Control non-native/problematic plants to restore habitat
https://www.conservationevidence.com/actions/2530
- We found no studies that evaluated the effects on mammals of controlling invasive or problematic plants to restore habitat.
‘We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Invasive plant species can drive large scale changes to habitats. These changes can make habitats less suitable for use by mammal species. Control of invasive or problematic plants might be undertaken to recreate suitable conditions for fauna, including target mammals (e.g. Dumalisile Somers 2017).
Dumalisile L. & Somers M.J. (2017) The effects of an invasive alien plant (Chromolaena odorata) on large African mammals. Nature Conservation Research, 2, 102–108, https://doi.org/10.24189/ncr.2017.048
9.9. Reintroduce top predators to suppress and reduce the impacts of smaller non-native predator and prey species
https://www.conservationevidence.com/actions/2531
- We found no studies that evaluated the effects on mammals of reintroducing top predators to suppress and reduce the impacts of smaller non-native predator and prey species.
’We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Small and medium-sized non-native predators can have severe detrimental impacts on native fauna, including mammals (e.g. Doherty et al. 2017). Some evidence suggests that their numbers can be reduced, to the benefit of native fauna, if top predator conservation is promoted, such as through reintroductions (e.g. Nimmo et al. 2015).
Nimmo D.G., Watson S.J., Forsyth D.M. & Bradshaw C.J.A. (2015) Dingoes can help conserve wildlife and our methods can tell. Journal of Applied Ecology, 52, 281–285.
Doherty T.S., Dickman C.R., Johnson C.N., Legge S.M., Ritchie E.G. & Woinarski J.C.Z. (2017) Impacts and management of feral cats Felis catus in Australia. Mammal Review, 47, 83–97.
9.10. Control non-native prey species to reduce populations and impacts of non-native predators
https://www.conservationevidence.com/actions/2532
- We found no studies that evaluated the effects on mammals of controlling non-native prey species to reduce populations and impacts of non-native predators.
’We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
The impact of non-native predators on native mammals can be more severe than that of native predators (Salo et al. 2007). Non-native predators may also feed on non-native prey and, in some situations, reducing non-native prey availability may lead to reductions in numbers of their non-native predators (Murphy et al. 1998; Mutze et al. 2017). This has potential to reduce the impact of non-native predators on native mammalian prey species.
Murphy E.C., Clapperton B.K., Bradfield P.M.F. & Speed H.J. (1998) Effects of rat-poisoning operations on abundance and diet of mustelids in New Zealand podocarp forests. New Zealand Journal of Zoology, 25, 315–328.
Salo P., Korpimäki E., Banks P.B., Nordström M. & Dickman C.R. (2007) Alien predators are more dangerous than native predators to prey populations. Proceedings of the Royal Society B, 274, 1237–1243, https://doi.org/10.1098/rspb.2006.0444
Mutze G. (2017) Continental-scale analysis of feral cat diet in Australia, prey-switching and the risk: benefit of rabbit control. Journal of Biogeography, 44, 1679–1681, https://doi.org/10.1111/jbi.12859
9.11. Provide artificial refuges for prey to evade/escape non-native predators
https://www.conservationevidence.com/actions/2533
- We found no studies that evaluated the effects on mammals of providing artificial refuges for prey to evade/escape non-native predators.
‘We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
This intervention considers use of small scale refuges rather than larger predator-free areas protected by fences. Artificial refuges, such as small shelters in otherwise open landscapes, could provide cover for native mammals to escape predation. Refuges are more often employed for reptile conservation, though at least one study found that they were insufficient to mitigate effects of non-native predators (Lettink et al. 2010). For mammals, refuges might entail small shelters, boxes or artificial burrows.
See also: Habitat restoration and creation — Provide artificial refuges/breeding sites.
Lettink M., Norbury G., Cree A., Seddon P.J., Duncan R.P., Schwarz C.J. (2010) Removal of introduced predators, but not artificial refuge supplementation, increases skink survival in coastal duneland. Biological Conservation, 143, 72–77, https://doi.org/10.1016/j.biocon.2009.09.004
9.12. Remove/control non-native species that could interbreed with native species
https://www.conservationevidence.com/actions/2534
- We found no studies that evaluated the effects on mammals of removing or controlling non-native species that could interbreed with native species.
’We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Hybridisation of non-native mammals with closely related native species can threaten local populations (e.g. Biedrzycka et al. 2020; Nussberger et al. 2014). Attempts may be made to reduce the risk through carrying out lethal control of the non-native species. The strategy can be difficult to execute, due to difficulties in separating hybrids from parent species.
Biedrzycka A., Solarz W. & Okarma H. (2012) Hybridization between native and introduced species of deer in Eastern Europe. Journal of Mammalogy, 93, 1331–1341, https://doi.org/10.1644/11-mamm-a-022.1
Nussberger B., Wandeler P., Weber D. & Keller L.F. (2014) Monitoring introgression in European wildcats in the Swiss Jura. Conservation Genetics, 15, 1219–1230, https://doi.org/10.1007/s10592-014-0613-0
9.13. Modify traps used in the control/eradication of non-native species to avoid injury of non-target mammal
https://www.conservationevidence.com/actions/2535
- One study evaluated the effects of modifying traps used in the control or eradication of non-native species to avoid injury of non-target mammals. This study was in the USA1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Condition (1 study): A before-and-after study in the USA1 found that modifying traps used for catching non-native mammals reduced moderate but not severe injuries among incidentally captured San Nicolas Island foxes.
BEHAVIOUR (0 STUDIES)
Background
A range of live-trapping techniques is used in control activities aimed at non-native species. As traps may capture species additional to the targeted non-native species, using live traps enables release of those non-target captures. However, restrained mammals are at risk of suffering injuries prior to being released. This intervention considers cases where modifications might be made to live traps with the intention of reducing such incidental injuries.
A before-and-after study in 2006–2010 on an offshore island in California, USA (1) found that modifying traps used to control non-native cats Felis catus reduced moderate but not severe injuries among San Nicolas Island foxes Urocyon littoralis dickeyi. These results were not tested for statistical significance. A lower proportion of San Nicolas Island foxes that were caught in modified traps (4%) suffered moderate injuries than when unmodified traps were used (25%). However, the rates of severe and very severe injuries in San Nicolas Island foxes were similar (around 5%) between the periods when modified and unmodified traps were used. The study was conducted on a 5,896-ha island. During 20 days in 2006, sixty-four San Nicolas Island foxes were caught with leg-hold traps deployed to catch non-native cats. Between June 2009 and January 2010, using modified leg-hold traps, 1,011 Nicolas Island foxes were caught. Trap modifications included a shorter anchor cable and chain, lighter spring, and additional swivels to allow unrestricted rotation of the trapped animal. Traps were checked remotely 24 hours a day to reduce the time foxes spent in the traps.
(1) Jolley W.J., Campbell K.J., Holmes N.D., Garcelon D.K., Hanson C.C., Will D., Keitt B.S., Smith G. & Little A.E. (2012) Reducing the impacts of leg hold trapping on critically endangered foxes by modified traps and conditioned trap aversion on San Nicolas Island, California, USA. Conservation Evidence, 9, 43–49.
9.14. Use conditioned taste aversion to prevent non-target species from entering traps
https://www.conservationevidence.com/actions/2536
- One study evaluated the effects on mammals of using conditioned taste aversion to prevent non-target species from entering traps. This study was in the USA1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (0 STUDIES)
BEHAVIOUR (1 STUDY)
- Behaviour change (1 study): A replicated, controlled study in the USA1 found that using bait laced with lithium chloride reduced the rate of entry of San Clemente Island foxes into traps set for feral cats.
Background
Animals may be trapped for a variety of reasons. In cases, such as where trapping is aimed at non-native species, a large number of traps might be set across the landscape. If there is a risk of catching non-target species, these will typically be live traps, from which individuals of non-target species can be released. However, trapping of animals usually entails at least some risk of injury to the animal as well as further risks, such as keeping parents away from their young. Furthermore, a trap holding a non-target animal is generally not then available for capturing the target animal until next visited by an operator. Conditioned taste aversion may be attempted, to try to make non-target mammals that are at risk of capture avoid traps because they associate them with an unpleasant taste or sensation.
A replicated, controlled study in 1992–1993 on an island in California, USA (1) found that lacing bait with lithium chloride reduced the rate of entry of San Clemente Island foxes Urocyon littoralis clementae into traps for feral cats Felis catus. In the first year, fewer foxes were recaptured using lithium chloride bait in traps (at 200 mg dose/kg of fox -9% recaught) than using unlaced bait (52% recaught). In the second year, fewer foxes were recaptured in traps using lithium chloride bait (3% recaught) than using unlaced bait (30% recaught). In sites where lithium chloride bait was used for 41 days and then switched to non-laced baits, recapture rates remained low for around 10 days after the switch, and then increased. Baits were placed in cage traps on a 146-km2 island. In 1992, two areas received lithium chloride baits (which induce gastrointestinal discomfort) and unlaced baits were used in three areas. In 1993, two areas received lithium chloride baits which were then switched to unlaced baits after 41 days and seven areas received unlaced baits throughout. Eight to 20 traps were used/area. Baits comprised 50 g of mixed cat food, tuna and raw hamburger, placed in traps from February through to July–August in 1992–1993.
(1) Phillips R.B. & Winchell C.S. (2011) Reducing nontarget recaptures of an endangered predator using conditioned aversion and reward removal. Journal of Applied Ecology, 48, 1501–1507, https://doi.org/10.1111/j.1365-2664.2011.02044.x
9.15. Use reward removal to prevent non-target species from entering traps
https://www.conservationevidence.com/actions/2537
- One study evaluated the effects on mammals of using reward removal to prevent non-target species from entering traps. This study was in the USA1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (0 STUDIES)
BEHAVIOUR (1 STUDY)
- Behaviour change (1 study): A replicated, controlled study in the USA1 found that when reward removal was practiced, the rate of San Clemente Island fox entry into traps set for feral cats was reduced.
Background
Animals may be trapped for a variety of reasons. In some cases, such as where trapping is aimed at non-native species, a large number of traps might be set across the landscape. If there is a risk of catching non-target species, these will typically be live traps, from which individuals of non-target species can be released. However, trapping of animals usually entails at least some risk of injury to the animal as well as further risks, such as keeping parents away from their young. Furthermore, a trap holding a non-target animal is generally not then available for capturing the target animal until next visited by an operator. Reward removal may be attempted, whereby strong-smelling bait is left in a form or situation where it is unavailable to animals, to consume. The intention is that non-target species will learn not to pursue that smell.
A replicated, controlled study in 1992 and 1994 on an island in California, USA (1) found that providing inaccessible bait inside a perforated can conditioned San Clemente Island foxes Urocyon littoralis clementae to avoid feral cat Felis catus traps. In the first year, fewer foxes were recaptured in traps with perforated can baits (8% recaught) than with accessible baits (52%). In the second year, fewer foxes were recaptured in traps using perforated can baits (1% recaptured) than those using accessible baits (27%). When bait treatments were switched between areas, recapture rates increased in those then receiving accessible bait and fell in those with perforated cans. Cat capture efficiency remained high throughout trials. Baits were placed in 8–20 cage traps/area on a 146-km2 island. In 1992, perforated can baits were used in two areas and accessible baits were used in three areas. In 1994, two areas received perforated can baits and accessible baits were used in three areas. Treatments were swapped over in these five areas after 41 days. Inaccessible baits were perforated cat food canisters (1992) or perforated plastic canisters containing cat food, tuna, raw hamburger and a fish oil scent (1994). Accessible baits were cat food, tuna and raw hamburger. Baits were used in traps from February through to June–July in 1992 and 1994.
(1) Phillips R.B. & Winchell C.S. (2011) Reducing nontarget recaptures of an endangered predator using conditioned aversion and reward removal. Journal of Applied Ecology, 48, 1501–1507, https://doi.org/10.1111/j.1365-2664.2011.02044.x
Problematic Native Species/Diseases
9.16. Remove or control predators
https://www.conservationevidence.com/actions/2613
- Ten studies evaluated the effects on non-controlled mammals of removing or controlling predators. Seven studies were in North America2,5–10, one was in Finland1, one in Portugal3 and one in Mexico4.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (10 STUDIES)
- Abundance (6 studies): Three of six studies (including three controlled, one before-and-after and one replicated, paired sites study), in Finland1 Portugal3, Mexico4 and the USA2,5,6, found that removing predators increased abundances of pronghorns5, moose6 and European rabbits and Iberian hares3. One of these studies also found that mule deer abundance did not increase5. The other three studies found that removing predators did not increase mountain hare1, caribou2 or desert bighorn sheep abundance.
- Reproductive success (2 studies): Two replicated, before-and-after studies (one also controlled), in the USA5,8, found that predator removal was associated with increased breeding productivity of white-tailed deer8 and less of a productivity decline in pronghorns5. However, one of these studies also found that there was no change in breeding productivity of mule deer3.
- Survival (5 studies): Two of five before-and-after studies (including two controlled studies and one replicated study), in the USA2,6,7, Canada10 and the USA and Canada combined9, found that controlling predators did not increase survival of caribou calves2, or of calf or adult female caribou9. Two studies found that moose calf survival6 and woodland caribou calf survival10 increased with predator control. The other study found mixed results with increases in white-tailed deer calf survival in some but not all years with predator control7.
BEHAVIOUR (0 STUDIES)
Background
Predators can limit population sizes of prey species. Changes in habitat or land management can lead to increases in predator populations which might negatively affect prey. Removing or controlling predators, especially native predators, for the benefit of their wild prey species can be a controversial management strategy. In many situations, it is more likely to occur for game management than directly for species conservation. Nonetheless, there is potential for such management to lead to increases in the abundance, survival or reproduction success of prey species.
A replicated, paired sites, controlled study in 1993–1998 of boreal forest in three areas in Finland (1) found that removing predators did not increase numbers of mountain hares Lepus timidus. In two of three areas, mountain hare numbers increased in both predator removal and predator protection sites, with the rate of increase being higher in the predator protection site than the removal site in one of those areas. In the third area, hare numbers declined each year in predator removal sites but increased in two of five years in protection sites. Data are presented as track count indices. In each of three areas, a predator removal and predator protection site were established, ≥5 km apart. Sites each covered 48–116 km2. Predator removal, carried out by hunters during normal hunting seasons, commenced in August 1993, targeting red fox Vulpes vulpes, pine marten Martes martes, stoat Mustela ermine and raccoon dog Nyctereutes procyonoides. Hares were monitored by snow track counts, annually from 15 January to 15 March, in 1993–1998.
A controlled, before-and-after study in 1990–2000 in alpine tundra and subalpine shrubland in Alaska, USA (2) found that wolf Canis lupus culling did not increase calf survival or population size of caribou Rangifer tarandus. Between 1992–1993 (before the wolf cull) and 1994–1995 (after the cull), the increase in calf:cow ratio within the cull area (before: 7.4:100; after: 21.5:100) was no greater than in a similar sized herd in an area without wolf culling (before: 11.2:100; after: 19.5:100). However, the change was greater than in a smaller sized herd in an area without wolf culling, where the calf:cow ratio declined (before: 15.8:100; after: 11.5:100). The long-term (1993–2000) change in caribou numbers in the population where wolves were controlled (before: 3,661; after: 3,227) was comparable to the population change in one of the areas without culling (before: 1,970; after: 1,730), but not to the other (before: 500; after: 675), although no statistical tests were carried out. Autumn calf:cow ratios were monitored annually between 1990 and 2000 from a helicopter, guided by radio-collared females. See original paper for methods for estimating population size. In 1993–1994, 60–62% of wolves were controlled by trapping, snaring and shooting. Smaller numbers (20–40%) were culled in subsequent years by local hunters.
A replicated, paired sites study in 2000–2001 of 24 games estates and hunting areas in Alentejo, Portugal (3) found that controlling predators resulted in greater numbers of European rabbits Oryctolagus cuniculus and Iberian hares Lepus granatensis. Game estates that controlled predators had a greater number of European rabbits (5.9 rabbits/10 km) and Iberian hares (1.7 hares/10 km) than paired hunting areas without predator control (0.5 rabbits/10 km; 0.3 hares/10 km). Twelve game estates that controlled predators (with box traps, shooting, snares) for >3 years were paired with 12 hunting areas without predator control. Paired sites (average 12 km2) were mostly grazed woodlands and farmland. Species controlled were red foxes Vulpes vulpes (11 estates), Egyptian mongooses Herpestes ichneumon (six estates), feral cats Felis catus and dogs Canis familiaris (two estates), common genets Genetta genetta (one estate), stone martens Martes foina (one estate) and azure-winged magpies Cyanopica cyanus (one estate). Each site within a pair was sampled once on consecutive days in May–June 2000 or 2001. Rabbits and hares and/or their signs (faeces, footprints) were counted along walked transects (average 12 km long).
A replicated study in 1951–2007 in nine desert sites in Arizona and New Mexico, USA, and the Gulf of California, Mexico (4) found that controlling mountain lions Puma concolor did not increase the population size of desert bighorn sheep Ovis canadensis. No bighorn sheep populations at sites where mountain lions were controlled increased in size (data not presented). Data were obtained from historical records for 10 sites with long-term survey and hunting information. Data included counts of bighorn sheep from both surveys and hunter harvests, and annual mountain lion harvests. No information on the number of mountain lions controlled is provided.
A replicated, paired sites, controlled, before-and-after study in 2007–2008 in 12 rangeland sites in Wyoming and Utah, USA (5) found that after coyotes Canis latrans were removed, pronghorn Antilocapra americana abundance was higher and productivity declined less in removal than non-removal sites, but for mule deer Odocoileus hemionus abundance and productivity did not differ. After eight months of coyote control, the abundance of pronghorn was higher and decline in productivity smaller in removal (abundance: 4.4 pronghorn/km2; change in productivity: -6.5 fawns/100 adult females) than in non-removal sites (abundance: 2.5 pronghorn/km2; change in productivity: -22 fawns/100 adult females). However, mule deer abundance and productivity did not differ between removal (abundance: 3.5 mule deer/km2; productivity: 56 fawns/100 adult females) and non-removal sites (abundance: 4.9 mule deer/km2; productivity: 62 fawns/100 adult females). Six pairs of sites in similar habitat were selected. Site areas totalled 10,517 km2. Between late July 2007 and March 2008, an average of 195 coyotes/1,000 km2 were removed from one site in each pair by trapping and shooting. Pronghorn and mule deer were counted by driving 17–27 km-long transects at 25 km/hr weekly during July and August and fortnightly in September, in 2007 and 2008.
A before-and-after study in 2001–2007 in a mosaic of shrub, forest and taiga in Alaska, USA (6) found that control of American black bear Ursus americanus, brown bear Ursus arctos and wolf Canis lupus increased moose Alces alces abundance and calf survival. Moose abundance and calf survival were higher after predator control (abundance: 0.56 moose/km2; calf/adult ratio: 51–63 calves/100 adult females) than before control (abundance: 0.38 moose/km2; calf/adult ratio: 34 calves/100 adult females). In May 2003 and 2004, 109 black and nine brown bears were translocated at least 240 km from a 1,368-km2 area, reducing the populations by approximately 96% and 50% respectively. In 200–2008, wolf numbers were reduced by 11–33 animals/year across a wider 8,314-km2 area by aircraft-assisted shooting, conventional hunting and trapping (density in 2001: 5.1 wolves/1,000 km2; density in 2006: 1.3 wolves/1,000 km2). Aircraft surveys (3.1 min/km2) were used to monitor moose numbers and calf/adult ratios annually, in autumn, at 87 sites within the study area, each of 15.7 km2.
A replicated, before-and-after study in 2006–2012 in three forest sites in South Carolina, USA (7) found that control of coyotes Canis latrans increased fawn survival in white-tailed deer Odocoileus virginianus in two out of three years. The annual survival rate of deer calves was higher one year (0.51) and three years (0.43) after the start of coyote control than before control (0.23), but did not differ two years (0.20) after the start of coyote control. The percentage of fawn mortalities that resulted from predation by coyotes was similar after (73%) compared to before control (80%). Between mid-January and early April 2010–2012, four hundred and seventy-four coyotes were removed from three 32-km2 sites (1.6 coyotes /km2/year) by trapping. The survival of 216 fawns (91 before and 125 after coyote control) was monitored using motion-sensitive radio-collars. Calves were monitored every eight hours if younger than four weeks, 1–3 times/day up to 12 weeks of age, weekly up to 16 weeks and 1–4 times/month up to 12 months.
A replicated, before-and-after study in 2010–2013 in two forest sites in Georgia, USA (8) found that controlling coyotes Canis latrans increased the number of young white-tailed deer Odocoileus virginianus relative to adult females in one of two sites. In one of two sites the number of young white-tailed deer was higher after coyote control (1.01 fawns/adult female) compared to before control (0.63 fawns/adult female). However, in one site there was no significant difference (after control: 0.85 fawns/adult female; before control: 0.84 fawns/adult female). Coyote abundance was lower after control (4–16 animals/site) than before control (16–21 animals/site). In March–June 2011, professional trappers controlled coyotes in both sites. In January and February of 2010–2013, infrared cameras were arranged in a grid pattern, over a 2,000-ha area, at a density of 1 camera/65 ha at each site. Cameras were baited with corn and took a photograph every 15 minutes for 10 days. The number of pictures of young deer relative to pictures of adult females was calculated.
A before-and-after study in 1994–2002 in a large forest and shrubland area in Alaska, USA and Yukon, Canada (9) found that trapping and removing or sterilizing wolves Canis lupus did not reduce caribou Rangifer tarandus mortality. The annual mortality of caribou calves (≤1 year old) did not differ after wolf removal or sterilization commenced (50–67%) compared to before (39–65%). Adult female (≥1 year old) annual mortality was also similar after wolf removal or sterilization commenced (9–10%) compared to before (9%). In a 50,000-km2 study area, 52–78 newborn caribou calves/year were radio-collared in May 1994–2002. Caribou were monitored during ≥3 flights/year. In 15 wolf packs, the dominant pair was sterilized in November 1997 and remaining wolves in those packs were translocated, mainly in April 1998. Eight additional packs were similarly treated over the following two winters. Caribou mortality was measured over four years before and five years after wolf control commenced.
A controlled, before-and-after study in 2008–2013 in four boreal forest, peatland and heath sites in Newfoundland, Canada (10) found that controlling coyotes Canis latrans increased caribou Rangifer tarandus calf survival. Caribou calf survival was higher when coyotes were controlled (70-day survival: 41%; 182-day survival: 32%) compared to before coyote control was carried out (70-day survival: 9%; 182-day survival: 7%). Survival rates across these two periods at sites without coyote control were stable (70-day survival: 52–58%; 182-day survival: 47%). At one site (covering 480 km2), lethal neck snares were set in March or April of 2012 and 2013 and were removed one week before caribou calving commenced in May. Forty coyotes were removed over these two years. Coyotes were not controlled at three other caribou calving sites. Caribou calves were radio-collared in late May to early June of 2008–2009 (193 calves) and 2012–2013 (103 calves), when 1–5-days old, and were monitored by radio-tracking through to November.
(1) Kauhala K., Helle P., Helle E. & Korhonen J. (1999) Impact of predator removal on predator and mountain hare populations in Finland. Annales Zoologici Fennici, 36, 139–148.
(2) Valkenburg P., McNay M.E. & Dale B.W. (2004) Calf mortality and population growth in the Delta caribou herd after wolf control. Wildlife Society Bulletin, 32, 746–756, https://doi.org/10.2193/0091-7648(2004)032[0746:cmapgi]2.0.co;2
(3) Beja P., Gordinho L., Reino L., Loureiro F., Santos-Reis M., & Borralho R. (2009) Predator abundance in relation to small game management in southern Portugal: conservation implications. European Journal of Wildlife Research, 55, 227–238, https://doi.org/10.1007/s10344-008-0236-1
(4) Wakeling BF., Lee R., Brown D., Thompson R., Tluczek M. & Weisenberger M. (2009) The restoration of desert bighorn sheep in the Southwest, 1951–2007: factors influencing success. Desert Bighorn Council Transactions, 50, 1–17.
(5) Brown D.E. & Conover M.R. (2011) Effects of large‐scale removal of coyotes on pronghorn and mule deer productivity and abundance. The Journal of Wildlife Management, 75, 876–882, https://doi.org/10.1002/jwmg.126
(6) Keech M.A., Lindberg M.S., Boertje R.D., Valkenburg P., Taras B.D., Boudreau T.A. & Beckmen K. B. (2011) Effects of predator treatments, individual traits, and environment on moose survival in Alaska. The Journal of Wildlife Management, 75, 1361–1380, https://doi.org/10.1002/jwmg.188
(7) Kilgo J.C., Vukovich M., Ray H.S., Shaw C.E. & Ruth C. (2014) Coyote removal, understory cover, and survival of white‐tailed deer neonates. The Journal of Wildlife Management, 78, 1261–1271, https://doi.org/10.1002/jwmg.764
(8) Gulsby W.D., Killmaster C.H., Bowers J.W., Kelly J.D., Sacks B.N., Statham M.J. & Miller K.V. (2015) White‐tailed deer fawn recruitment before and after experimental coyote removals in central Georgia. Wildlife Society Bulletin, 39, 248–255, https://doi.org/10.1002/wsb.534
(9) Boertje R.D., Gardner C.L., Ellis M.M., Bentzen T.W. & Gross J.A. (2017) Demography of an increasing caribou herd with restricted wolf control. The Journal of Wildlife Management, 81, 429–448, https://doi.org/10.1002/jwmg.21209
(10) Lewis K.P., Gullage S.E., Fifield D.A., Jennings D.H. & Mahoney S.P. (2017) Manipulations of black bear and coyote affect caribou calf survival. The Journal of Wildlife Management, 81, 122–132, https://doi.org/10.1002/jwmg.21174
9.17. Sterilize predators
https://www.conservationevidence.com/actions/2573
- One study evaluated the effects on potential prey mammals of sterilizing predators. This study was in the USA and Canada1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Survival (1 study): A before-and-after study in the USA and Canada1 found that sterilising some wolves (combined with trapping and removing others) did not increase caribou survival.
BEHAVIOUR (0 STUDIES)
Background
Predators can limit population sizes of prey species. Changes in habitat or land management can lead to increases in predator populations which might negatively affect prey. Removing or controlling predators, especially native predators, for the benefit of their wild prey species can be a controversial management strategy. Nonetheless, there is potential for such management to lead to increases in the abundance, survival or reproduction success of prey species. Sterilization of predators may be proposed as an alternative strategy that may be regarded as being more acceptable than removal or lethal control.
A before-and-after study in 1994–2002 in a large forest and shrubland area in Alaska, USA and Yukon, Canada (1) found that sterilising some wolves Canis lupus (and trapping and removing others) did not reduce caribou Rangifer tarandus mortality. The annual mortality of caribou calves (≤1 year old) did not differ after wolf sterilization and removal commenced (50–67%) compared to before (39–65%). Adult female (≥1 year old) annual mortality was also similar after wolf sterilization and removal commenced (9–10%) compared to before (9%). In a 50,000-km2 study area, 52–78 newborn caribou calves/year were radio-collared in May 1994–2002. In fifteen wolf packs, the dominant pair was sterilized in November 1997 and remaining wolves in those packs were translocated, mainly in April 1998. Eight additional packs were similarly treated over the following two winters. Caribou mortality was measured over four years before and five after wolf control commenced during ≥3 aerial surveys/year.
(1) Boertje R.D., Gardner C.L., Ellis M.M., Bentzen T.W. & Gross J.A. (2017) Demography of an increasing caribou herd with restricted wolf control. The Journal of Wildlife Management, 81, 429–448, https://doi.org/10.1002/jwmg.21209
9.18. Remove or control competitors
https://www.conservationevidence.com/actions/2575
- Two studies evaluated the effects on non-controlled mammals of removing or controlling competitors. One study was across Norway and Sweden1 and one was in Norway2.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Reproductive success (1 study): A replicated, controlled study in Norway and Sweden1 found that red fox control, along with supplementary feeding, was associated with an increase in arctic fox litters.
BEHAVIOUR (1 STUDY)
- Use (1 study): A controlled study in Norway2 found that where red foxes had been controlled arctic foxes were more likely to colonize.
Background
The range occupied by a species may be limited by the presence of competitors. In many cases, removing native competitors may be a controversial management strategy. However, abundance increases or range expansion of a competitor species, due to habitat or land management changes, may motivate removal or control of this species if its presence negatively impacts on another species that is deemed to be a higher conservation priority.
A replicated, controlled study in 1999–2011 at 10 tundra sites in Norway and Sweden (1) found that the number of arctic fox Vulpes lagopus litters increased after control of red foxes Vulpes vulpes, along with supplementary winter feeding at arctic fox dens. Where red foxes were intensively controlled, the number of active artic fox dens in winter increased more than at sites where no control or a low level of control was undertaken (data reported as statistical model results). The same response was found in the number of arctic fox litters produced, and with more litters produced when food was provided at den sites (data reported as statistical model results). Three sites were intensive control sites, with an average of 19–92 red foxes culled, and supplementary feeding provided for an average of 11–13.5 arctic fox dens at two of those sites. Three sites had low levels of control, with 1.5–7 red foxes culled and 1–3 dens fed at each of those sites. Four sites had no fox control and only one den was fed at one site. Red foxes were controlled during winter from 1999. The number of arctic fox litters was counted in known arctic fox dens during July and August 1999–2011.
A controlled study in 2005–2010 in 25 tundra sites in Finnmark, Norway (2) found that the probability of colonization by arctic fox Vulpes lagopus was higher in sites where red foxes Vulpes vulpes had been controlled. Arctic foxes colonized some sites where red foxes were controlled but their probability of colonizing sites without fox control was zero (reported as statistical model results). Between 2005 and 2010, intensive culling removed 885 red foxes from the Varanger peninsula. Foxes were monitored annually, over a 2-month period in late winter, using automatic digital cameras in front of a frozen block of reindeer remains. Fifteen camera sites were located across the area where red foxes were controlled and 10 areas without control (Nordkynn peninsula and Ifjordfjellet). Each camera took photographs of the carcass and its close surroundings every 10 min.
(1) Angerbjörn A., Eide N.E., Dalén L., Elmhagen B., Hellström P., Ims R.A., Killengreen S., Landa A., Meijer T., Mela M. & Niemimaa J. (2013) Carnivore conservation in practice: replicated management actions on a large spatial scale. Journal of Applied Ecology, 50, 59–67, https://doi.org/10.1111/1365-2664.12033
(2) Hamel S., Killengreen S.T., Henden J.A., Yoccoz N.G. & Ims R.A. (2013) Disentangling the importance of interspecific competition, food availability, and habitat in species occupancy: recolonization of the endangered Fennoscandian arctic fox. Biological Conservation, 160, 114–120, https://doi.org/10.1016/j.biocon.2013.01.011
9.19. Provide diversionary feeding for predators
https://www.conservationevidence.com/actions/2578
- One study evaluated the effects on potential prey mammals of providing diversionary feeding for predators. This study was in Canada1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Survival (1 study): A controlled, before-and-after study in Canada1 found that diversionary feeding of predators appeared to increase woodland caribou calf survival.
BEHAVIOUR (0 STUDIES)
Background
Predators can limit population sizes of prey species. Changes in habitat or land management can lead to increases in predator populations, which might negatively affect prey. Removing or controlling predators, especially native predators, for the benefit of their wild prey species can be a controversial management strategy. Nonetheless, there is potential for reduced predator activities to lead to increases in the abundance, survival or reproductive success of prey species. Supplementary feeding of predators may be proposed as an alternative strategy that may be regarded as being more acceptable than removal or lethal control.
A controlled, before-and-after study in 2008–2011 in four boreal forest, peatland and heath sites in Newfoundland, Canada (1) found that diversionary feeding of predators appeared to increase woodland caribou Rangifer tarandus calf survival. However, the significance of the intervention was not explicitly tested. Caribou calf survival during diversionary feeding (70-day survival: 23%; 182-day survival: 14%) appeared to be higher than before diversionary feeding commenced (70-day survival: 9%; 182-day survival: 7%) though there was high variability in these data. Survival rates across these two periods at sites without diversionary feeding were stable (70-day survival: 56–59%; 182-day survival: 41–47%). Supplementary food was mostly taken by American black bears Ursus americanus which, along with coyotes Canis latrans, were the most frequent confirmed predators of caribou calves. At one site, 500-kg bags of bakery waste were distributed in a grid of 4.5 × 4.3-km quadrats, covering most of the caribou calving area. Food was provided from before 25 May until mid-July in 2010 and 2011 and was replenished weekly as required. In 2011, food was supplemented with beaver Castor canadensis carcasses. Three other caribou calving sites received no supplementary food. Across all sites, 313 caribou calves were radio-collared in late May to early June of 2008–2011, when 1–5 days old, and were monitored by radio-tracking through to November.
(1) Lewis K.P., Gullage S.E., Fifield D.A., Jennings D.H. & Mahoney S.P. (2017) Manipulations of black bear and coyote affect caribou calf survival. The Journal of Wildlife Management, 81, 122–132, https://doi.org/10.1002/jwmg.21174
9.20. Sterilise non-native domestic or feral species (e.g. cats and dogs)
https://www.conservationevidence.com/actions/2579
- We found no studies that evaluated the effects on mammals of sterilising non-native domestic or feral species (e.g. cats and dogs).
’We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Domestic animals may present a range of problems for wild mammals. These can include predation (e.g. Woods et al. 2013), disease transmission and hybridization between closely related species (Nussberger et al. 2014). Culling (especially feral animals) may be an option for reducing these threats but can be controversial on animal rights or animal welfare grounds. Sterilizing such animals is an alternative strategy that may reduce impacts of non-native species in the longer term and may also be possible to achieve on a large scale among domestic animals, by liaising with their owners.
Woods M., Mcdonald R. & Harris S. (2003) Predation of wildlife by domestic cats Felis catus in Great Britain. Mammal Review, 33, 174–188, https://doi.org/10.1046/j.1365-2907.2003.00017.x
Nussberger B., Wandeler P., Weber D. & Keller L.F. (2014) Monitoring introgression in European wildcats in the Swiss Jura. Conservation Genetics, 15, 1219–1230, https://doi.org/10.1007/s10592-014-0613-0
9.21. Train mammals to avoid problematic species
https://www.conservationevidence.com/actions/2580
- Two studies evaluated the effects of training mammals to avoid problematic species. Both studies were in Australia1a,1b.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Survival (1 study): A controlled study in Australia1b found that training greater bilbies to avoid introduced predators did not increase their post-release survival.
BEHAVIOUR (2 STUDIES)
- Behaviour change (2 studies): One of two controlled studies in Australia found that greater bilbies trained to avoid introduced predators showed more predator avoidance behaviour1a, the second study found no difference in behaviour between trained and untrained bilbies1b.
Background
Mammals raised in areas free of non-native predators may be poorly adapted for use in translocations into areas where they have a greater chance of encountering such predators. This intervention includes cases where attempts are made to expose them to non-native predator cues with the intent that they will be able to avoid these after release. This intervention covers specifically training attempts on wild-born mammals. For captive-born mammals, see: Species management — Train captive-bred mammals to avoid predators.
A controlled study in 2005 in a desert reserve in South Australia, Australia (1a) found that greater bilbies Macrotis lagotis which had been trained to avoid invasive mammalian predators showed more predator avoidance behaviour than bilbies which had not received such training. Seven bilbies which had been trained to avoid predators changed burrow more frequently (5.7 times in 11 nights) than seven bilbies without such training (1.4 times). Trained bilbies also moved further between successive burrows (trained: 1,387 m; untrained: 158 m) and selected burrows with more entrance holes (trained: 3.6 entrances; untrained: 2.2 entrances) than untrained individuals. Additionally, all seven trained bilbies changed burrow the night after cat Felis catus scent was sprayed at their burrow entrance, but none of the untrained bilbies changed burrow. In May–June 2005, 14 bilbies were caught in a predator-free area of the Arid Recovery Reserve. Upon capture, seven individuals were exposed to a mock attack by a cat carcass and to cat urine and faecal matter and seven were not. Bilbies were then released at the capture site. All bilbies were equipped with microchips and radio-transmitters. Bilbies were radio-tracked daily to locate their diurnal burrow. Three days after capture, bilbies were located in their diurnal burrows and cat scent was sprayed at the entrance within four hours of sunset.
A controlled study in 2007–2009 in a desert reserve in South Australia, Australia (1b) found that post-release survival and predator avoidance behaviour of greater bilbies Macrotis lagotis with and without training to avoid invasive mammalian predators did not differ. Nine of 10 bilbies trained to avoid predators and eight of 10 without such training survived over six months after release. The trained bilby that died was either predated or scavenged by a wedge-tailed eagle Aquila audax. One bilby without training was killed by a cat Felis catus and one died of natural causes. Four months after release, the number of bilbies which changed burrow the night after cat scent was sprayed at their burrow entrance was the same for trained and untrained individuals (3 of 5 bilbies in each group). The population became extinct 19 months after release. In August 2007, twenty bilbies were caught in a predator-free area of the Arid Recovery Reserve and released, within three hours, into a 200-km2 unfenced area with invasive cats and foxes Vulpes vulpes. Upon capture, 10 individuals were exposed to a mock attack by a cat carcass and to cat urine and faecal matter and 10 were not. All bilbies were equipped with radio-transmitters. Daily attempts were made to locate bilbies during the first month and weekly mortality checks were made for at least the following six months. Four months after release, bilbies were located in their diurnal burrows and cat scent was sprayed at the entrance within four hours of sunset.
(1) Moseby K.E., Cameron A. & Crisp H.A. (2012) Can predator avoidance training improve reintroduction outcomes for the greater bilby in arid Australia? Animal Behaviour, 83, 1011–1021, https://doi.org/10.1016/j.anbehav.2012.01.023
9.22. Treat disease in wild mammals
https://www.conservationevidence.com/actions/2581
- Three studies evaluated the effects on mammals of treating disease in the wild. Two studies were in the USA2,3 and one was in Germany1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (2 STUDIES)
- Condition (2 studies): A replicated study in Germany1 found that medical treatment of mouflons against foot rot disease healed most infected animals. A before-and-after study in the USA2 found that management which included vaccination of Yellowstone bison did not reduce prevalence of brucellosis.
BEHAVIOUR (1 STUDY)
- Uptake (1 study): A study in the USA3 found that a molasses-based bait was readily consumed by white-tailed deer, including when it contained a dose of a disease vaccination.
Background
Treatment of diseases in wild mammals can be problematic. It can be difficult to diagnose causes of illness and the administration of medicines directly to target individuals can be challenging. Except in cases of highly threatened species, treatment of disease in wild mammals is usually only carried out when there are potential economic costs of not treating, such as a risk of transmission to domestic animals or reductions in numbers or health of animals that have sporting value. This intervention includes cases where animals are confined for treatment (and one study on captive animals that trials a delivery mechanism for treatments that might be administered to wild mammals) but in all cases, the aim is to improve the health of wild populations.
See also: Use vaccination programme.
A replicated study in 1994–2005 in three forest sites in Hessen and Rheinland-Pfalz, Germany (1) found that medical treatment of mouflons Ovis gmelini musimon against foot rot disease healed most infected animals. No statistical analyses were performed. All 152 infected individuals fully treated for foot rot disease recovered with no signs of reinfection. No data are provided for 13 individuals that only received partial treatment. Two hundred and fifty mouflons were caught using a fenced kraal or net trap and kept in a corral for six weeks. All were injected with penicilline–streptomycine (1–3 ml of Tardomyocel III comp®), had an anti-parasitic treatment (0.2 mg/kg of Ivomec®) and, in cases of bad general condition (e.g. fever) a supplementary treatment was administered (see paper for details). A total of 165 animals with foot rot were treated by trimming the wounded hooves and covering them in antiseptic fluid (Kodan®-Tincture). Some were treated with an additional antibiotic injection (5.0 ml Procain Penicillin G® solution). If needed, a second treatment was conducted after two or three days. Four to six weeks after treatment, a final trimming of the hooves was undertaken before the animals were released.
A before-and-after study in 2001–2010 on grasslands in and around a national park in Wyoming, USA (2) found that intensive management, including vaccination, of Yellowstone bison Bison bison bison did not reduce prevalence of brucellosis Brucella abortus. The proportion of adult female bison testing positive for brucellosis increased or remained constant during the period at approximately 60%. However, transmission of brucellosis from bison to domestic cattle was almost eliminated. Bison were intensively managed, which included separating them from cattle on winter pastures, herding them into the park in spring, and periodic culls where these aims could not be achieved. A proportion of bison was tested for brucellosis and animals that tested positive were slaughtered. Bison, especially adult females, were vaccinated either when captured or by remote vaccine delivery. During 2001–2010, 1,643 bison that tested positive for brucellosis were slaughtered and 18 were released. A total of 1,517 bison that tested negative or were untested were also slaughtered. The overall population ranged from 2,432 to 5,015 during this period.
A study in 2012 on captive animals in Iowa, USA (3) found that white-tailed deer Odocoileus virginianus readily consumed a molasses-based bait, including when it contained a dose of a disease vaccination. In 48 of 50 trials, all baits were consumed within three hours. However, on >62% of occasions, all baits in one serving were consumed by a single deer. All baits containing Mycobacterium bovis bacillus Calmette–Guerin (BCG) vaccine were consumed. Baits, containing flour, cane molasses, sugar, water, shortening, sodium bicarbonate and sodium chloride, were baked into 8-g pellets. Seven pellets were fed to deer in addition to their usual feed, in each of five pens (three each containing three deer, one with four deer and one with 50 deer) daily for 10 days. Consumption was observed using camera traps. Additionally, five baits containing 0.2 ml BCG were offered to three deer during January 2012, in addition to their usual feed.
(1) Volmer K., Hecht W., Weiß R. & Grauheding D. (2008) Treatment of foot rot in free-ranging mouflon (Ovis gmelini musimon) populations—does it make sense? European Journal of Wildlife Research, 54, 657–665, https://doi.org/10.1007/s10344-008-0192-9
(2) White P.J., Wallen R.L., Geremia C., Treanor J.T. & Blanton D.W. (2011) Management of Yellowstone bison and brucellosis transmission risk — Implications for conservation and restoration. Biological Conservation, 144, 1322–1334, https://doi.org/10.1016/j.biocon.2011.01.003
(3) Palmer M.V., Stafne M.R., Waters W.R., Thacker T.C. & Phillips G.E. (2014) Testing a molasses-based bait for oral vaccination of white-tailed deer (Odocoileus virginianus) against Mycobacterium bovis. European Journal of Wildlife Research, 60, 265–270, https://doi.org/10.1007/s10344-013-0777-9
9.23. Use vaccination programme
https://www.conservationevidence.com/actions/2582
- Seven studies evaluated the effects on mammals of using vaccination programmes. Three studies were in the UK5a,5b,6 and one study was in each of Belgium1, Spain2, Poland3 and Ethiopia4.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (7 STUDIES)
- Abundance (1 study): A before-and-after study in Poland3 found that following an anti-rabies vaccination programme, red fox numbers increased.
- Condition (6 studies): Five studies (including three replicated, three controlled and two before-and-after studies) in Belgium1, Spain2 and the UK5a,5b,6 found that following vaccination, rabies was less frequent in red foxes1, numbers of Eurasian badgers5a,5b,6 infected with tuberculosis was reduced and European rabbits2 developed immunity to myxomatosis and rabbit haemorrhagic disease. One of the studies5a also found that vaccination reduced the speed and extent of infection in infected Eurasian badgers. A study in Ethiopia4 found that following vaccination of Ethiopian wolves, a rabies outbreak halted.
BEHAVIOUR (0 STUDIES)
Background
Vaccinating wild mammals can be challenging, due to difficulties in administering vaccines in appropriate doses to target animals. Only in particular cases, such as when animals may be affected by a zoonotic disease, that could spread to humans or domestic livestock, or when particularly endangered mammal populations are threatened, is vaccination likely to be attempted.
A study in 1989–1991 in a rural region of Luxembourg, southern Belgium (1) found that vaccinating red foxes Vulpes vulpes against rabies reduced the occurrence of rabies. After one vaccination attempt, six out of nine (67%) rabid and 11 of 14 (79%) healthy foxes tested had consumed the bait. After the second attempt, 25 of 31 (81%) adult foxes and 27 of 55 (49%) juvenile foxes tested had consumed bait, and all 86 were healthy. After the third vaccination phase, 64 of 79 (81%) foxes had consumed bait and only one tested positive for rabies (authors note that it was found at the edge of the vaccination area, and had not taken bait). Additionally, the number of cases of rabies reported in livestock every six months fell from 7–61 before the second vaccination attempt (January 1985–June 1990) to zero in the year afterwards (reporting of rabies in livestock is mandatory in Belgium). In November 1989, April 1990 and October 1990, a total of 25,000 field vaccine-baits containing VVTGgRAB and a tetracycline biomarker were dropped by helicopter across a 2,200 km2 area at a density of 15/km (excluding urban areas). After each vaccination period (January–March 1990, April–October 1990, November 1990–April 1991) a total of 188 foxes which were found dead or shot by hunters were tested for both rabies and the presence of tetracycline (which would indicate that they had consumed the bait).
A replicated, before-and-after study in 1999–2002 in Cadiz province, Spain (2) found that most vaccinated European wild rabbits Oryctolagus cuniculus developed immunity to myxomatosis and rabbit haemorrhagic disease. Of 32 rabbits which initially had no immunity to myxomatosis, 26 (81%) had developed immunity 2–4 weeks after vaccination. Of 81 rabbits which initially had no immunity to rabbit haemorrhagic disease, 68 (84%) had developed immunity 2–4 weeks after vaccination. The development of immunity did not differ between males and females, nor did it vary with time spent in captivity. Between November 1999 and March 2002, six groups of 14–46 wild-caught rabbits (some of which already had natural immunity to one or both diseases) were vaccinated against myxomatosis and rabbit haemorrhagic disease with commercial vaccines, and held in captivity for two, three or four weeks. Blood samples were taken from each rabbit both before vaccination, and two days prior to release, to test for immunity to each disease.
A before-and-after study in 1980–2005 in a rural area near Rogów, Central Poland (3) found that following an anti-rabies vaccination programme, red fox Vulpes vulpes numbers increased. The density of fox tracks was higher after the start of the vaccination programme than before (11.0 vs 5.9 snow tracks/km/day). The same pattern held for fox density as recorded by surveys from vehicles (2.6 vs 1.2 foxes/km2) and for active dens (15.0 vs 9.3 dens with young/year). However, there were fewer cubs/den after vaccination (3.4) than before (3.8). Anti-rabies vaccinations started in 1995–1996. Between 1980 and 2005, fox densities were estimated annually within an 89-km2 area. Estimates were from counts of tracks in snow (average annual transect length was 90 km before and 55 km after the vaccination programme), individuals seen from vehicles in forest habitats, and location of dens and number of cubs within the dens.
A study in 2003–2004 in alpine habitat in a national park in Ethiopia (4) found that vaccinating Ethiopian wolves Canis simensis successfully halted a rabies outbreak. Of 69 wolves vaccinated in the ‘intervention zone’ (beyond the boundaries of the outbreak) between one to four months after rabies was confirmed, all 19 animals sampled one month later had protective levels of rabies antibodies. Six months after initial vaccinations, two wolves that received a booster vaccination at 30 days still had protective levels of antibodies while one wolf that did not receive a booster had levels below those regarded as providing protection. Of five wolves sampled 12 months after initial vaccinations, one that received a booster still had protective levels of rabies antibodies while four that received only initial vaccinations did not have protective levels. The last confirmed rabies death was two months after the start of the vaccination programme. Rabies was first confirmed on 28 October 2003 from wolf mortalities since mid-August. Sixty-nine wolves were vaccinated in the intervention zone, between November 2003 and February 2004. A further eight were vaccinated during follow-up recapture (March–November 2004). Mortality in the affected sub-population was 76%.
A replicated, controlled study in 2006–2009 on 15 wild-caught, captive Eurasian badgers Meles meles in England, UK (5a) found that vaccinating badgers against tuberculosis reduced the likelihood of tuberculosis infection, and reduced both the speed and the extent of infection in infected animals. Three out of nine badgers vaccinated with Bacillus Calmette-Guérin (BCG) became infected with tuberculosis, compared to six out of six badgers which had not been vaccinated. The time taken for infection to develop was longer in vaccinated badgers (two, eight and 12 weeks), than in non-vaccinated badgers (2–4 weeks). Vaccinated badgers had fewer lesions (median score: 4) than non-vaccinated badgers (median score: 9–12.5). Fifteen tuberculosis-free wild badgers were caught and housed in groups of up to four. Nine badgers were injected with 1 ml of Bacillus Calmette-Guérin (BCG) Danish strain 1331 vaccine and six were not vaccinated. After 17 weeks, all 15 badgers were infected with tuberculosis. Every 2–3 weeks badgers were anaesthetized and examined for tuberculosis infection and, 29 weeks after vaccination, the badgers were killed and examined for tuberculosis infection. (Years of study assumed from information provided, as not specified).
A replicated, randomized, controlled study in 2006–2009 in an area of mixed woodland and farmland in Gloucestershire, UK (5b, same experimental set-up as 6) found that vaccinating Eurasian badgers Meles meles against tuberculosis reduced the number of animals infected. Vaccination with Bacillus Calmette-Guérin (BCG) reduced the number of badgers with tuberculosis in vaccinated groups (15/179 infected, 8%) compared to non-vaccinated groups (18/83 infected, 22%). In 2009, badgers were caught in cage traps, set for two consecutive nights, twice a year, at every active sett in a 55 km2 study area. Badgers were tested for tuberculosis using three tests. Social groups were randomly allocated to ‘vaccinated’ or ‘not vaccinated’ treatments. Every badger caught in a vaccination group was injected with 1 ml of Bacillus Calmette-Guérin (BCG) Danish strain 1331 vaccine once per year. A total of 179 badgers from 38 social groups were vaccinated, while 83 badgers from 26 social groups were unvaccinated.
A randomized, controlled, before-and-after study in 2006–2009 in an area of mixed woodland and farmland in Gloucestershire, UK (6, same experimental set-up as 5b) found that vaccinating Eurasian badgers Meles meles against tuberculosis reduced the number of animals infected. Three years after vaccination with Bacillus Calmette-Guérin (BCG) began, the number of badgers infected with tuberculosis (119 of 342 tested, 35%) was lower than before vaccination began (156 of 294 tested, 53%). Vaccination reduced the likelihood of individual badgers testing positive for tuberculosis by 54%. Unvaccinated badgers from vaccinated social groups were less likely to have tuberculosis (adults: 35%, cubs: 21% infected) than badgers from unvaccinated social groups (adults: 52%, cubs: 33% infected). Additionally, unvaccinated cubs were 79% less likely to become infected with tuberculosis when at least one third of the adults in their social group were vaccinated. However the probability of an unvaccinated adult having tuberculosis did not change when more group members were vaccinated. From June 2006–October 2009, badgers were caught in baited steel mesh traps, set for two consecutive nights, twice a year at every active sett in a 55 km2 study area. Badgers were tested for tuberculosis using three tests. Social groups were randomly allocated to ‘vaccinated’ or ‘not vaccinated’ treatments. Badgers in vaccination groups were injected with 1 ml of Bacillus Calmette-Guérin (BCG) Danish strain 1331 vaccine once/year.
(1) Brochier B., Kieny M.P., Costy F., Coppens P., Bauduin B., Lecocq J.P., Languet B., Chappuis G., Desmettre P., Afiademanyo K., Libois R. & Pastoret P.-P. (1991) Large-scale eradication of rabies using recombinant vaccinia-rabies vaccine. Nature, 354, 520–522.
(2) Cabezas S., Calvete C. & Moreno S. (2006) Vaccination success and body condition in the European wild rabbit: applications for conservation strategies. Journal of Wildlife Management, 70, 1125–1131, https://doi.org/10.2193/0022-541x(2006)70[1125:vsabci]2.0.co;2
(3) Goszczyński J., Misiorowska M. & Juszko S. (2008) Changes in the density and spatial distribution of red fox dens and cub numbers in central Poland following rabies vaccination. Acta Theriologica, 53, 121–127, https://doi.org/10.1007/bf03194245
(4) Knobel D.L., Fooks A.R., Brookes S.M., Randall D.A., Williams S.D., Argaw K., Shiferaw F., Tallents L.A. & Laurenson M.K. (2008) Trapping and vaccination of endangered Ethiopian wolves to control an outbreak of rabies. Journal of Applied Ecology, 45, 109–116, https://doi.org/10.1111/j.1365-2664.2007.01387.x
(5) Chambers M.A., Rogers F., Delahay R.J., Lesellier S., Ashford R., Dalley D., Gowtage S., Davé D., Palmer S., Brewer J., Crawshaw T., Clifton-Hadley R., Carter S., Cheeseman C., Hanks C., Murray A., Palphramand K., Pietravalle S., Smith G.C., Tomlinson A., Walker N.J., Wilson G.J., Corner L.A.L., Rushton S.P., Shirley M.D.F., Gettinby G., McDonald R.A. & Hewinson R.G. (2011) Bacillus Calmette-Guérin vaccination reduces the severity and progression of tuberculosis in badgers. Proceedings of the Royal Society of Biology, 278, 1913–1920.
(6) Carter S.P., Chambers M.A., Rushton S.P., Shirley M.D.F. Schuchert P., Pietravalle S., Murray A., Rogers F., Gettinby G., Smith G.C., Delahay R.J., Hewinson R.G. & McDonald R.A. (2012) BCG vaccination reduces risk of tuberculosis infection in vaccinated badgers and unvaccinated badger cubs. PLoS One, 7, e49833, https://doi.org/10.1371/journal.pone.0049833
9.24. Eliminate highly virulent diseases early in an epidemic by culling all individuals (healthy and infected) in a defined area
https://www.conservationevidence.com/actions/2585
- We found no studies that evaluated the effects on mammals of eliminating highly virulent diseases early in an epidemic by culling all individuals (healthy and infected) in a defined area.
’We found no studies’ means that we have not yet found any studies that have directly evaluated this intervention during our systematic journal and report searches. Therefore, we have no evidence to indicate whether or not the intervention has any desirable or harmful effects.
Background
Culling is a well-established approach for the management of some diseases in domestic animals, and although it has been used in an attempt to eliminate disease or reduce rates of transmission in a range of wild mammal species (Carter et al. 2009), the culling of diseased wild mammals for conservation is rarely attempted, probably due to ethical and ecological considerations (Woodroffe 1999). Nonetheless, prompt culling of all animals in an area might have potential to control or eliminate disease outbreaks and reduce longer-term negative impacts of disease on populations (McCallum 2008).
Carter S.P., Roy, S.S., Ji, W.H., Cowan, D.P., Smith, G.C., Delahay, R.J., Rossi, S. and Woodroffe, R. (2008) Options for the control of disease 2: Targeting hosts. Pages 121–146 in: R.J. Delahay, G.C. Smith & M.R. Hutchings (eds) Management of disease in wild mammals. Springer, UK, https://doi.org/10.1007/978-4-431-77134-0_7
Woodroffe R. (1999) Managing disease threats to wild mammals. Animal Conservation, 2, 185–193, https://doi.org/10.1111/j.1469-1795.1999.tb00064.x
McCallum H. (2008) Tasmanian devil facial tumour disease: lessons for conservation biology. Trends in Ecology and Evolution, 23, 631–637, https://doi.org/10.1016/j.tree.2008.07.001
9.25. Cull disease-infected animals
https://www.conservationevidence.com/actions/2586
- One study evaluated the effects on mammals of culling disease-infected animals. This study was in Tasmania1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Condition (1 study): A before-and-after, site comparison study in Tasmania1 found that culling disease-infected Tasmanian devils resulted in fewer animals with large tumours associated with late stages of the disease.
BEHAVIOUR (0 STUDIES)
Background
When mammal populations are threatened by disease, one potential action is to remove contact between diseased and disease-free animals. However, it is rarely attempted, possibly due to ethical and ecological concerns (Woodroffe 1999).
Woodroffe R. (1999) Managing disease threats to wild mammals. Animal Conservation, 2, 185–193, https://doi.org/10.1111/j.1469-1795.1999.tb00064.x
A before-and-after and site comparison study in 2004–2007 on two peninsulas in Tasmania (1) found that culling disease-infected Tasmanian devils Sarcophilus harrisii resulted in fewer animals with large tumours associated with late stages of the disease. One year after intensive culling commenced, the proportion of trapped Tasmanian devils with large tumours (22%) was lower than during the first month of intensive culling (67%; numbers not reported). Tasmanian devil density remained constant during this time (1.6 devils/km2) compared to a similar site without culling where density declined (from 0.9 to 0.6 devils/km2), although statistical tests were not carried out. Tasmanian devils infected with Devil Facial Tumour Disease were culled during an 18-month pilot study commencing in June 2004, and an intensive 12-month trapping program commencing in January 2006. Tasmanian devils were trapped within a 160-km2 area on the peninsula during 4–5 x 10-day trips/year. Infected individuals or those with signs of the disease were euthanized. Numbers with large tumours (>4 cm) were counted in February 2006 and January 2007. Tasmanian devil density was recorded in the study area and at a similar 160-km2 peninsula on the same coast (methods not reported).
(1) Jones M.E., Jarman P.J., Lees C.M., Hesterman H., Hamede R.K., Mooney N.J., Mann D., Pukk C.E., Bergfield J. & McCallum H. (2007) Conservation Management of Tasmanian Devils in the Context of an Emerging, Extinction-threatening Disease: Devil Facial Tumor Disease. EcoHealth, 4, 326–337, https://doi.org/10.1007/s10393-007-0120-6
9.26. Use drugs to treat parasites
https://www.conservationevidence.com/actions/2587
- Seven studies evaluated the effects on mammals of using drugs to treat parasites. Three studies were in the USA2,3,4, two were in Spain5a,5b, one was in Germany1 and one was in Croatia6.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (7 STUDIES)
- Survival (1 study): A randomized, replicated, controlled study the USA4 found that medical treatment of Rocky Mountain bighorn sheep against lungworm did not increase lamb survival.
- Condition (6 studies): Three of four before-and-after studies (one controlled), in Germany1, the USA2,3 and Croatia6, found that after administering drugs to mammals, parasite burdens were reduced in roe deer1 and in wild boar piglets6 and numbers of white-tailed deer3 infected were reduced. A third study found that levels of lungworm larvae in bighorn sheep faeces were reduced one month after drug treatment but not after three to seven months2. One of these studies also found that the drug treatment resulted in increased body weight in roe deer fawns1. A replicated, controlled, before-and-after study in Spain5a found that higher doses of ivermectin treated sarcoptic mange in Spanish ibex faster than lower doses, and treatment was more effective in animals with less severe infections. A replicated, before-and-after study in Spain5b found that after injecting Spanish ibex with ivermectin to treat sarcoptic mange a mange-free herd was established.
BEHAVIOUR (0 STUDIES)
Background
High levels of parasites in wild mammals may reduce fitness and lead to higher levels of mortality (e.g. Cooper et al. 2012). Drugs are readily available to reduce infestation levels of a wide range of parasites, though they are more frequently used to treat domestic animals. Attempts to treat wild mammals are most likely to be made where there is specific economic value to the wild mammal, such as among species that are valued for sporting purposes. In such cases, drug treatments may be administered through adding to baits or supplementary food left for animals.
Cooper N., Kamilar J.M. & Nunn C.L. (2012) Host longevity and parasite species richness in mammals. PLoS ONE, 7, e42190, https://doi.org/10.1371/journal.pone.0042190
A before-and-after study in 1979–1986 in a forest area in Middle Rhine, Germany (1) found that supplementing food with a drug to reduce parasitic worms reduced parasite burdens and increased body weights in roe deer Capreolus capreolus. After seven years of treatment, nematode burdens were reduced by 95% in fawns and 99% in adult deer, compared to levels before treatments began. Average weights of fawns killed for venison increased during this time to 9.4 kg, from 4.9 kg prior to treatment with the drug. Following discovery of high nematode burdens and associated mortality in 1979, winter fodder of deer (bran, mill leftovers and maize silage) was supplemented with anthelmintic powder (Fenbendazole, containing 4% Panacur) for seven years in a dose of 5 mg/kg body weight. Parasite burdens were assessed from faecal samples and from 90 carcasses collected before and 57 after treatments.
A replicated, controlled, before-and-after study in 1987–1988 in a state park in South Dakota, USA (2) found that following medical treatment, lungworm larvae levels in bighorn sheep Ovis canadensis faeces reduced over the following month, but not 3–7 months after treatment. In the month following treatment, average concentrations of lungworm larvae in faeces of bighorn sheep treated with one dose (50–250 larvae/g faeces) or two doses of ivermectin (50–300 larvae/g faeces) were lower than in untreated sheep (500–1,400 larvae/g faeces). However, by 3–7 months after treatments, average concentrations of lungworm larvae did not differ significantly between treated (600–1,300 larvae/g faeces) and untreated sheep (300–600 larvae/g faeces). One group of free-ranging female sheep received alfalfa treated with the anti-parasitic drug ivermectin in February 1987 and 1988 (four and six individuals, respectively) and another group received it in both February and March 1987 and January and February 1988 (seven and 14 sheep respectively). Five (1987) and nine (1988) sheep were untreated. Each treatment was administrated over two successive days at a rate of 2 ml ivermectin/sheep, and sheep were pre-baited with untreated alfalfa two weeks prior to each treatment. Parasite counts were made through analysing sheep faeces collected weekly from January to March and June to August in 1987–1988.
A controlled, before-and-after study in 1987–1989 in a grassland wildlife refuge in Texas, USA (3) found that feeding white-tailed deer Odocoileus virginianus medicated corn reduced trematode Fascioloides magna parasite infection by 63%. Four weeks after treatment with triclabendazole, fewer white-tailed deer were infected with live parasites (2/23) than in baited control (15/24) and unbaited control areas (24/30). Before treatment, the number of infected deer was similar (area to be treated: 8/9; baited control: 4/8; unbaited control: 5/8). In winter 1987–1989, at each of 10 sites across a 391-ha treatment pasture and 10 sites across 421-ha of baited control pasture, untreated corn was distributed for 3–4 weeks, before corn containing triclabendazole (500 ml triclabendazole/23 kg corn) was used in the treatment pasture for a further week. The estimated dose was 11 mg/kg body weight/deer/day for seven days. Corn was placed at dusk, and deer were counted at each bait site between 2100–2300 hr. At a third, 439-ha unbaited control pasture, no corn was distributed. In January 1987, before baiting began, 13 fawns and 12 adult deer were shot across the three areas. In 1987–1989, four weeks after baiting finished, 6–15 adult deer were shot on each pasture. The liver of each deer was examined for parasites.
A randomized, replicated, controlled study in 1991–1995 in two mountain ranges in Colorado, USA (4) found that medical treatment of Rocky Mountain bighorn sheep Ovis canadensis canadensis against lungworm did not increase lamb survival. Average annual recruitment did not differ between herds treated for lungworm (0.5–0.7 lambs/adult female) and untreated herds (0.6–0.7 lambs/adult female). Adult bighorn females of four herds were captured in February–March 1991–1995 and were marked and radio-collared. Between 1991 and 1995 the herds were either fed for 8–10 weeks each winter with 2 kg/individual/day of alfalfa hay and 1 kg/individual/day of apple pulp, fed with alfalfa hay and apple pulp with two treatments of a drug to reduce parasitic worms (Fenbendazole, 3 g/adult female) added to the apple pulp late in the feeding period, given Fenbendazole-treated salt blocks (1.65 g Fenbendazole/kg) from December to April, or not given food or Fenbendazole-treated salt blocks. Treatments were rotated annually under a predetermined, randomly selected scheme. Lamb survival for 11–18 marked adult females/herd was assessed every two weeks between May and October.
A replicated, controlled, before-and-after study in 1988 in a mountainous National Park in southern Spain (5a) found that injecting Spanish ibex Capra pyrenaica hispanica with higher doses of ivermectin treated sarcoptic mange Sarcoptes scabiei faster than lower doses, and treatment was more effective in animals with less severe infections. All nine ibex with limited mange recovered after being treated with ivermectin. Six animals injected with 0.4 mg/kg body weight had no scabs or mites 21 days after treatment, and three animals injected with 0.2 mg/kg body weight had no scabs or mites four and five weeks after treatment, respectively. However, only three of six ibex with severe infection recovered following treatment, and two died. The sixth animal was still carrying mites two months after treatment. From September–December 1988, wild Spanish ibex were caught, sedated, and treated with Foxim anti-mange treatment (500 mg/l of water). Fifteen adult (>2-years old) female ibex with sarcoptic mange were divided into five treatment groups: 1) ibex with limited mange, given a single dose of ivermectin (0.4 mg/kg body weight) by syringe injection; 2) ibex with limited mange given a single dose of ivermectin (0.4 mg/kg body weight) by rifle dart injection; 3) ibex with limited mange given a single dose of ivermectin (0.2 mg/kg body weight) by syringe; 4) ibex with severe mange given two doses of ivermectin (0.2 mg/kg body weight) by syringe, two weeks apart; 5) ibex with severe mange given two doses of ivermectin (0.4 mg/kg body weight) by syringe, two weeks apart. Infection was classified into four levels of severity, and treatment tested on the worst two: limited (‘consolidation’: affected skin limited to a few body parts) and severe (‘chronic’: severe skin disease covering much of the body). Ibex were examined for two months to monitor recovery.
A replicated, before-and-after study in 1989 in a mountainous National Park in southern Spain (5b) found that after injecting Spanish ibex Capra pyrenaica hispanica with ivermectin to treat sarcoptic mange Sarcoptes scabiei, a mange-free herd was established. All 32 Spanish ibex treated with ivermectin showed no signs of mange six weeks after treatment began. After joining 65 mange-free ibex (at least 12 of which were treated in an earlier program, and 17 of which were mange-free on capture), the total population of 97 ibex showed no signs of mange for at least a year. From February–March 1989, sixty-three Spanish ibex were caught, sedated and examined for sarcoptic mange. The 14 ibex with chronic mange were injected with ivermectin (0.4 mg/kg body weight) and released at the capture site. The 49 remaining ibex, including healthy animals, were injected with ivermectin (0.4 mg/kg body weight) and a foxim spray (500 mg/l), and examined for mites. The 17 animals without mites were placed in ‘quarantine’ pens, and 32 with mites were kept in ‘treatment’ pens and injected with ivermectin (0.2 mg/kg body weight) two-and four-weeks later before joining the ‘quarantine’ pens. After two weeks in quarantine, ibex showing no symptoms of mange were given a final dose of ivermectin and released into a 400-ha enclosure in Nava de San Pedro Park which already contained 48 ibex.
A replicated, before-and-after study in three sites in Slavonia, Croatia (6) found that using drugs to treat parasites reduced the number of parasite eggs in the dung of wild boar Sus scrofa piglets. These results were not tested for statistical significance. After 14 days, parasite eggs were found in 0–10% of piglet faecal samples compared to 70–100% before treatment. The anti-parasitic drug ivermectin (0.6% formulation) was mixed with piglet feed at a concentration of 9 parts per million. An unspecified number of piglets in three sites were offered the feed for seven days using semi-automated piglet feeders, which were refilled twice each week. Faecal samples from the piglets were examined before the treatment and after seven and 14 days.
(1) Düwel D. (1987) Repeated treatment of roe deer (Capreolus capreolus) with Panacur in winter for control of nematode infection. Zeitschrift fur Jagdwissenschaft, 33, 242–248
(2) Easterly T.G., Jenkins K.J. & McCabe T.R. (1992) Efficacy of orally administered ivermectin on lungworm infection in free-ranging bighorn sheep. Wildlife Society Bulletin, 20, 34–39.
(3) Qureshi T., Drawe D.L., Davis D.S. & Craig T.M. (1994) Use of bait containing triclabendazole to treat Fascioloides magna infections in free-ranging white-tailed deer. Journal of Wildlife Diseases, 30, 346–350.
(4) Miller M.W., Vayhinger J.E., Bowden D.C., Roush S.P., Verry T.E., Torres A.N. & Jurgens V.D. (2000) Drug treatment for lungworm in bighorn sheep: reevaluation of a 20-year-old management prescription. The Journal of Wildlife Management, 64, 505–512, https://doi.org/10.2307/3803248
(5) León-Vizcaíno L., Cubero M.J., González-Capitel E., Simón M.A., Pérez L., de Ybáñez M.R.R., Ortíz J.M., Candela M.G. & Alonso F. (2001) Experimental ivermectin treatment of sarcoptic mange and establishment of a mange-free population of Spanish ibex. Journal of Wildlife Diseases, 37, 775–785, https://doi.org/10.7589/0090-3558-37.4.775
(6) Rajkovi-Janje R., Manojlovi L. & Gojmerac T. (2004) In-feed 0.6% ivermectin formulation for treatment of wild boar in the Moslavina hunting ground in Croatia. European Journal of Wildlife Research, 50, 41–43, https://doi.org/10.1007/s10344-003-0033-9
9.27. Establish populations isolated from disease
https://www.conservationevidence.com/actions/2588
- One study evaluated the effects on mammals of establishing populations isolated from disease. The study was in sub-Saharan Africa1.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Condition (1 study): A site comparison study throughout sub-Saharan Africa1 found that fencing reduced prevalence of canine distemper but not of rabies, coronavirus or canine parvovirus in African wild dogs.
BEHAVIOUR (0 STUDIES)
Background
When mammal populations are threatened by disease, a short-to medium-term management option may be to establish wild-living or captive populations that are isolated from sources of the disease, such as on islands or in large fenced enclosures (e.g. Jones et al. 2007). These could aid persistence of the species and provide stock for reintroductions, should the disease be eliminated or sufficiently controlled in the originally affected areas.
Jones M.E., Jarman P.J., Lees C.M., Hesterman H., Hamede R.K., Mooney N.J., Mann D., Pukk C,.E., Bergfeld J. & McCallum H. (2007) Conservation management of Tasmanian devils in the context of an emerging, extinction-threatening disease: devil facial tumor disease. EcoHealth, 4, 326–337, https://doi.org/10.1007/s10393-007-0120-6
A site comparison study in 1988–2010 of 16 sites throughout sub-Saharan Africa (1) found that fencing reduced prevalence of canine distemper but not of rabies, coronavirus or canine parvovirus in African wild dogs Lycaon pictus. Prevalence of canine distemper was lower in fenced protected sites (0.04 seroprevalence) than in unfenced protected sites (0.28) or unfenced and unprotected sites (0.20). However, the prevalence of rabies, coronavirus or parvovirus did not change significantly between fenced protected sites (rabies: 0.02; coronavirus: 0.03; parvovirus: 0.22 seroprevalence), unfenced protected sites (rabies: 0.06; coronavirus: 0.11; parvovirus: 0.19) and unfenced and unprotected sites (rabies: 0.12; coronavirus: 0.18; parvovirus: 0.21). Blood samples were collected from 268 African wild dogs in 1988–2009 across 16 sites representing five unconnected wild dog populations: South Africa (2 unconnected populations; 7 protected-fenced sites, 3 unprotected-unfenced), Zimbabwe, Botswana (1 population; 2 protected-unfenced site, 2 unprotected-unfenced), Tanzania (1 protected-unfenced site) and Kenya (1 unprotected-unfenced site). Protected-fenced sites had game fencing likely to exclude domestic dogs. Seroprevalence (proportion of animals with detectable antibodies against a disease) was determined from blood samples.
(1) Prager K.C., Mazet J.A.K., Munson L., Cleaveland S., Donnelly C.A., Dubovi E.J., Szykman Gunther M., Lines R., Mills G., Davies-Mostert H.T., Weldon McNutt J., Rasmussen G., Terio K., Woodroffe R. (2012) The effect of protected areas on pathogen exposure in endangered African wild dog (Lycaon pictus) populations. Biological Conservation, 150, 15–22, https://doi.org/10.1016/j.biocon.2012.03.005
9.28. Control ticks/fleas/lice in wild mammal populations
https://www.conservationevidence.com/actions/2589
- Two studies evaluated the effects of controlling ticks, fleas or lice in wild mammal populations. Both studies were in the USA1,2.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (2 STUDIES)
- Condition (2 studies): A replicated, paired sites, controlled study in the USA1 found that a grain-bait insecticide product did not consistently reduce flea burdens on Utah prairie dogs. A controlled study the USA2 found that treating wolves with ivermectin cleared them of infestations of biting dog lice.
BEHAVIOUR (0 STUDIES)
Background
Although the effects of parasites, such as ticks, fleas and lice, on their hosts are often undetectable, there can be serious adverse health effects of high parasite burdens, including reduced reproductive output and increased mortality (Wall 2007). Furthermore, in some cases, parasites can be carriers of disease that can have severe adverse effects on populations (e.g. Biggins & Kosoy 2001). Treatments, developed primarily for domestic animals, may be administered to wild mammals to reduce parasite burdens. The administering of such treatments, though, can be challenging.
Biggins D.E. & Kosoy M.Y. (2001) Influences of introduced plague on North American mammals: implications from ecology of plague in Asia. Journal of Mammalogy, 82, 906–916, https://doi.org/10.1644/1545-1542(2001)082 <0906:ioipon>2.0.co;2
Wall R. (2007) Ectoparasites: future challenges in a changing world. Veterinary Parasitology, 148, 62–74, https://doi.org/10.1016/j.vetpar.2007.05.011
A replicated, paired sites, controlled study in 2009–2010 on six grasslands in Utah, USA (1) found that following treatment with a grain-bait insecticide product, there was no consistent reduction in flea burdens on Utah prairie dogs Cynomys parvidens. After one summer, fewer fleas were recorded on prairie dogs in treated than untreated colonies at two sites, there was no difference at one site and more fleas were recorded in treated than untreated colonies at one site. After the second summer (with treatments applied twice) there were fewer fleas on prairie dogs in treated than untreated colonies at one site and no difference at two sites. See paper for full data. At six sites with prairie dog colonies, treatment and control plots were established, covering 2–190 ha, depending on animal density. Four sites were monitored in 2009 and three in 2010. In 2009, 56 g of imidacloprid-treated oat grain bait (Kaput®) was scattered within 2.4 m of each burrow in treatment colonies, once in May–June. Imidacloprid is an insecticide that can reduce burdens of fleas and, thus, reduce the risk of transmission of plague. In 2010, the treatment was applied twice, five days apart, in April–May. Prairie dogs were trapped monthly, using 100 live traps for five days in both treatment and control areas at each site, in June–October, and combed to count fleas.
A controlled study in 2002–2010 in a forested area of Alaska, USA (2) found that treating wolves Canis lupus with ivermectin cleared them of infestations of biting dog lice Trichodectes canis. All of 12–19 wolf packs treated with ivermectin, were lice-free in the winter following treatment. In spring, 15–50% of packs were infested over the three years of treatments, 5% were infested the following spring, with 0% spring infestation in the last two years of monitoring. Three untreated packs remained infested throughout four years of monitoring. In a 13,000-km2 study area, lice infestation in two packs was confirmed by inspecting animal hides harvested by trappers in 2002–2005. Moose or lynx meat, injected with ivermectin, was distributed aerially at den and rendezvous sites of 12–19 wolf packs at 10–20 day intervals in 2005–2007. Infestation status and responses to treatments were determined by live-trapping wolves, direct observations and by inspection of hides obtained from trappers during 2005–2010.
(1) Jachowski D.S., Brown N.L., Wehtje M., Tripp D.W., Millspaugh J.J. & Gompper M.E. (2012) Mitigating plague risk in Utah prairie dogs: Evaluation of a systemic flea‐control product. Wildlife Society Bulletin, 36, 167–175, https://doi.org/10.1002/wsb.107
(2) Gardner C.L., Beckmen K.B., Pamperin N.J. & Del Vecchio P. (2013) Experimental treatment of dog lice infestation in interior Alaska wolf packs. Wildlife Management, 77, 626–632, https://doi.org/10.1002/jwmg.495