▁This ▁may ▁have ▁been ▁the ▁result ▁of ▁past oral ists ▁abandon ing ▁their ▁settlement s , ▁and ▁thus ▁their ▁horses , ▁due ▁to ▁the ▁ar id ▁conditions ▁and ▁un famil iar ▁land ▁that ▁combined ▁to ▁make ▁far ming ▁in ▁Australia ▁especially ▁difficult . ▁After ▁World ▁War ▁I , ▁the ▁demand ▁for ▁horses ▁by ▁defence ▁forces ▁decl ined ▁with ▁the ▁growth ▁in ▁mechan ization , ▁which ▁led ▁to ▁a ▁growth ▁in ▁the ▁number ▁of ▁unw anted ▁animals ▁that ▁were ▁often ▁set ▁free . ▁Through out ▁the ▁ 2 0 th ▁century , ▁the ▁replacement ▁of ▁horses ▁with ▁machines ▁in ▁far ming ▁led ▁to ▁further ▁redu ctions ▁in ▁demand , ▁and ▁may ▁have ▁also ▁contributed ▁to ▁increases ▁in ▁fer al ▁populations . ▁ ▁Currently , ▁Australia ▁has ▁at ▁least ▁ 4 0 0 , 0 0 0 ▁horses ▁ro aming ▁the ▁continent . ▁It ▁is ▁also ▁estimated ▁that , ▁during ▁non - dr ought ▁periods , ▁the ▁fer al ▁horse ▁population ▁increases ▁at ▁a ▁rate ▁of ▁ 2 0 ▁percent ▁per ▁year . ▁Dr ought ▁conditions ▁and ▁br ush f ires ▁are ▁natural ▁thre ats . ▁Despite ▁population ▁numbers , ▁fer al ▁horses ▁are ▁generally ▁considered ▁to ▁be ▁a ▁moder ate ▁p est . ▁Where ▁they ▁are ▁allowed ▁to ▁damage ▁veget ation ▁and ▁cause ▁er os ion , ▁the ▁impact ▁on ▁the ▁environment ▁can ▁be ▁det r iment al , ▁and ▁for ▁that ▁reason ▁can ▁be ▁considered ▁a ▁serious ▁environmental ▁threat . ▁However , ▁because ▁they ▁also ▁have ▁cultural ▁and ▁potential ▁economic ▁value , ▁the