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Providing evidence to improve practice

Action: Use fencing to exclude grazers or other problematic species Terrestrial Mammal Conservation

Key messages

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  • Three studies evaluated the effects on mammals of using fencing to exclude grazers or other problematic species. One study was in each of the USA, Australia and Spain.

COMMUNITY RESPONSE (1 STUDY)

  • Richness/diversity (1 study): A controlled, before-and-after study in Australia 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 Spain and Australia found that using fences to exclude large or introduced herbivores increased the abundance of Algerian mice and native mammals. A replicated, paired sites study in the USA 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)

Supporting evidence from individual studies

1 

A replicated, paired sites study in 1994–1995 in the Western Mojave Desert, California, USA (Brooks 1999) 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.

2 

A controlled, before-and-after study in 2004–2007 in a woodland savannah in north-west Australia (Legge et al. 2011) 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.

3 

A replicated, controlled, paired sites study in 2010–2012 in Holm oak Quercus ilex woodland in Cabañeros National Park, Central Spain (Navarro-Castilla et al. 2017) 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.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.