The Ecology of Wild Horses and their Environmental ... - Parks Victoria

The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 20133.6 Impacts on faunaWild horse populations can alter the composition of bird, fish, crustacean, small mammal, reptile and antcommunities (Nimmo & Miller 2007) and have been identified as a major threat to a range of native wildlifespecies in the Victorian Alps. The 2001 AALC Natural Heritage Working Group Workshop of field staff andscientists, ranked wild horses as one of the top five priority fauna threats to the Australian Alps (Coyne 2001).Wild horses can affect native fauna through causing habitat modification or loss, and also through competitionfor resources (i.e. food, water, shelter and space) (Olsen & Low 2006; Nimmo & Miller 2007).3.6.1 Competition and altered food availabilityWild horses compete for resources with native herbivores, especially macropods, including: grey kangaroos(Macropus giganteus), red-necked wallabies (M.rufogriseus) and swamp wallabies (Wallabia bicolour). Variousstudies have demonstrated that high densities of wild horses correspond with reduced densities of macropods.Berman and Jarman (1988) found few signs of macropods in the Northern Territory in areas heavily grazed bywild horses. A study of wild horse impacts in Guy Fawkes River National Park by Lenehan (2010) providesevidence of wild horses displacing kangaroos from prime feeding habitats. Dung transects conducted in thenational park showed a strong negative relationship between wild horse dung and macropod dung. As wildhorses were removed from the transect area (as part of NSW National Parks and Wildlife Service (NPWS) horsecapture program, where 250 wild horses were removed) there was a significant progressive decline in horsedung and increase in macropod dung. Indicating that macropods were responding positively to decreases inhorse abundance (Lenehan 2010).Although it has not been investigated to date, it is possible that wild horses also compete with other nativemammals such as wombats (Vombatus ursinus). Wombats also feed primarily on grasses (such as Poa andother grass species and some shrubs) and like wild horses, dig below the snow to reach low vegetation duringwinter (Matthews 2010).Wild horse activity may constrain resources for many species and may increase the vulnerability of threatenedspecies (Nano et al. 2003). A reduction in the density of wild horses in Finke Gorge National Park andsurrounding area correlated with a striking increase in black-footed rock wallabies (Petrogale lateralis) andsmall fauna populations (Matthews et al. 2001). In 1990 no fresh black-footed rock wallaby dung wasrecorded, however after approximately 6000 wild horses were removed (and the population kept at lownumbers), the amount of fresh dung recorded steadily increased over the following ten years. It is suggestedthat the wild horse population may also have suppressed the endangered stick-nest rat (Zyzomyspedunculatus) in the West MacDonald ranges (Nano et al. 2003). Despite numerous surveys the species wasnot recorded between 1960 and 1996 and it was concluded the species was extinct. However in 1996 it wasrediscovered at numerous sites, a finding that corresponded with the removal of 30 000 wild horses (Nano etal. 2003). The major food plants identified in the diet of the stick-nest rat were also palatable to wild horsesand other introduced ungulates (ibid.).3.6.2 Habitat modificationWild horse grazing can result in a more open shrubland and increased area of bare ground, which in turncauses changes for associated wildlife (Zalba & Cozzani 2009). The removal of vegetation through grazing,trampling, wallowing and rubbing can result in a loss of shrub and ground vegetation connectivity. The habitatvalue of a site for animal species that require shrubs for shade, food or protection from predators and otherthreats may be reduced by the loss of this connectivity (Beever et al. 2008).Simplification of habitat by wild horses can lead to a reduction in foraging, nesting and roosting opportunitiesfor native animals, such as ground dwelling, foraging and roosting birds (O’Connor 2005). Zalba and Cozzani(2009) investigated the impact of wild horses on different bird communities in the Pampas grasslands in22