Action: Use fencing to exclude predators or other problematic species
Key messagesRead our guidance on Key messages before continuing
- Ten studies evaluated the effects on mammals of using fencing to exclude predators or other problematic species. Four studies were in Australia, four were in the USA and two were in Spain.
COMMUNITY RESPONSE (1 STUDY)
- Richness/diversity (1 study): A site comparison study in Australia 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 studies (including two replicated, controlled studies), in Spain, Australia and the USA, found that abundances of European rabbits and small mammals 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 fencing. A replicated, controlled study in Spain 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 USA 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 Spain, Australia and the USA, found that fencing to exclude predators did not increase survival of translocated European rabbits, hispid cotton rats, southern flying squirrels or western barred bandicoots. The other two studies found that persistence of populations of eastern barred bandicoots and long-haired rats was greater inside than outside fences. A controlled, before-and-after study in the USA found that electric fencing reduced coyote incursions into sites frequented by black-footed ferrets.
BEHAVIOUR (0 STUDIES)
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.
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.
Supporting evidence from individual studies
A replicated, controlled study in 2002–2003 in four grassland and shrubland sites in south-west Spain (Rouco et al. 2008) 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 (Winnard & Coulson 2008) 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 (Read & Cunningham 2010) 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 (Morris et al. 2011) 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 (Guerrero-Casado et al. 2013) 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 (Karmacharya et al. 2013) 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 (Matchett et al. 2013) 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 (Frank et al. 2014) found that fencing to exclude cats Felis sylvestris 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 (Conner et al. 2016) 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 (Short 2016) 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).
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- Frank A.S., Johnson C.N., Potts J.M., Fisher A., Lawes M.J., Woinarski J.C.Z., Tuft K., Radford I.J., Gordon I.J., Collis M.A., Legge S. & Frid C. (2014) Experimental evidence that feral cats cause local extirpation of small mammals in Australia's tropical savannas. Journal of Applied Ecology, 51, 1486-1493
- 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
- 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