<strong>The</strong> <strong>Ecology</strong> <strong>of</strong> <strong>Wild</strong> <strong>Horses</strong> <strong>and</strong> <strong>their</strong> <strong>Environmental</strong> Impact in the <strong>Victoria</strong>n Alps May 2013In 2011 the AALC commenced a project that aims to quantify the impacts <strong>of</strong> wild horses on upl<strong>and</strong> streams<strong>and</strong> wetl<strong>and</strong>s in the Australian Alps. <strong>The</strong> results <strong>of</strong> this study will be available in autumn 2013 <strong>and</strong> will providefurther evidence <strong>of</strong> the impacts <strong>of</strong> wild horses on sensitive stream <strong>and</strong> wetl<strong>and</strong> environments.Photo 7: <strong>Wild</strong> horse pugging <strong>of</strong> waterway resulting in bank slumping, Murray Headwaters (source: <strong>Parks</strong> <strong>Victoria</strong> 2006).Photo 8: <strong>Wild</strong> horse damage to Murray River water source (source: <strong>Parks</strong> <strong>Victoria</strong> 2006)Photo 9: <strong>Wild</strong> horse trampling at the head <strong>of</strong> Moscow Creek, Cobberas Range, ANP (source: <strong>Parks</strong> <strong>Victoria</strong> 2006).21
<strong>The</strong> <strong>Ecology</strong> <strong>of</strong> <strong>Wild</strong> <strong>Horses</strong> <strong>and</strong> <strong>their</strong> <strong>Environmental</strong> Impact in the <strong>Victoria</strong>n Alps May 20133.6 Impacts on fauna<strong>Wild</strong> horse populations can alter the composition <strong>of</strong> bird, fish, crustacean, small mammal, reptile <strong>and</strong> antcommunities (Nimmo & Miller 2007) <strong>and</strong> have been identified as a major threat to a range <strong>of</strong> native wildlifespecies in the <strong>Victoria</strong>n Alps. <strong>The</strong> 2001 AALC Natural Heritage Working Group Workshop <strong>of</strong> field staff <strong>and</strong>scientists, ranked wild horses as one <strong>of</strong> the top five priority fauna threats to the Australian Alps (Coyne 2001).<strong>Wild</strong> horses can affect native fauna through causing habitat modification or loss, <strong>and</strong> also through competitionfor resources (i.e. food, water, shelter <strong>and</strong> space) (Olsen & Low 2006; Nimmo & Miller 2007).3.6.1 Competition <strong>and</strong> altered food availability<strong>Wild</strong> horses compete for resources with native herbivores, especially macropods, including: grey kangaroos(Macropus giganteus), red-necked wallabies (M.rufogriseus) <strong>and</strong> swamp wallabies (Wallabia bicolour). Variousstudies have demonstrated that high densities <strong>of</strong> wild horses correspond with reduced densities <strong>of</strong> macropods.Berman <strong>and</strong> Jarman (1988) found few signs <strong>of</strong> macropods in the Northern Territory in areas heavily grazed bywild horses. A study <strong>of</strong> wild horse impacts in Guy Fawkes River National Park by Lenehan (2010) providesevidence <strong>of</strong> wild horses displacing kangaroos from prime feeding habitats. Dung transects conducted in thenational park showed a strong negative relationship between wild horse dung <strong>and</strong> macropod dung. As wildhorses were removed from the transect area (as part <strong>of</strong> NSW National <strong>Parks</strong> <strong>and</strong> <strong>Wild</strong>life Service (NPWS) horsecapture program, where 250 wild horses were removed) there was a significant progressive decline in horsedung <strong>and</strong> 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 <strong>and</strong>other grass species <strong>and</strong> some shrubs) <strong>and</strong> like wild horses, dig below the snow to reach low vegetation duringwinter (Matthews 2010).<strong>Wild</strong> horse activity may constrain resources for many species <strong>and</strong> may increase the vulnerability <strong>of</strong> threatenedspecies (Nano et al. 2003). A reduction in the density <strong>of</strong> wild horses in Finke Gorge National Park <strong>and</strong>surrounding area correlated with a striking increase in black-footed rock wallabies (Petrogale lateralis) <strong>and</strong>small fauna populations (Matthews et al. 2001). In 1990 no fresh black-footed rock wallaby dung wasrecorded, however after approximately 6000 wild horses were removed (<strong>and</strong> the population kept at lownumbers), the amount <strong>of</strong> 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 <strong>and</strong> 1996 <strong>and</strong> it was concluded the species was extinct. However in 1996 it wasrediscovered at numerous sites, a finding that corresponded with the removal <strong>of</strong> 30 000 wild horses (Nano etal. 2003). <strong>The</strong> major food plants identified in the diet <strong>of</strong> the stick-nest rat were also palatable to wild horses<strong>and</strong> other introduced ungulates (ibid.).3.6.2 Habitat modification<strong>Wild</strong> horse grazing can result in a more open shrubl<strong>and</strong> <strong>and</strong> increased area <strong>of</strong> bare ground, which in turncauses changes for associated wildlife (Zalba & Cozzani 2009). <strong>The</strong> removal <strong>of</strong> vegetation through grazing,trampling, wallowing <strong>and</strong> rubbing can result in a loss <strong>of</strong> shrub <strong>and</strong> ground vegetation connectivity. <strong>The</strong> habitatvalue <strong>of</strong> a site for animal species that require shrubs for shade, food or protection from predators <strong>and</strong> otherthreats may be reduced by the loss <strong>of</strong> this connectivity (Beever et al. 2008).Simplification <strong>of</strong> habitat by wild horses can lead to a reduction in foraging, nesting <strong>and</strong> roosting opportunitiesfor native animals, such as ground dwelling, foraging <strong>and</strong> roosting birds (O’Connor 2005). Zalba <strong>and</strong> Cozzani(2009) investigated the impact <strong>of</strong> wild horses on different bird communities in the Pampas grassl<strong>and</strong>s in22
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