▁which ▁they ▁feed , ▁as ▁well ▁as ▁alter ing ▁the ▁habitat ▁of ▁the ▁birds ▁and ▁their ▁pre y . ▁Fer al ▁horse ▁gra zing ▁is ▁also ▁linked ▁to ▁a ▁decl ine ▁in ▁re pt iles ▁and ▁am ph ib ians ▁due ▁to ▁habitat ▁loss . ▁In ▁addition , ▁the ▁gra zing ▁and ▁tram pling ▁near ▁water ways ▁influ ences ▁aqu atic ▁fa una . ▁In ▁areas ▁frequ ented ▁by ▁horses , ▁c rab ▁dens ities ▁are ▁higher , ▁increasing ▁the ▁prop ens ity ▁for ▁pred ation ▁on ▁fish . ▁As ▁a ▁result , ▁fish ▁dens ities ▁decl ine ▁as ▁the ▁removal ▁of ▁veget ation ▁rend ers ▁them ▁more ▁sus cept ible ▁to ▁pred ation . ▁ ▁In ▁areas ▁where ▁horses ▁are ▁abund ant , ▁mac rop od ▁populations ▁are ▁less ▁pre val ent . ▁This ▁is ▁most ▁likely ▁due ▁to ▁the ▁horses ’ ▁consumption ▁of ▁veget ation ▁upon ▁which ▁the ▁mac rop ods ▁normally ▁feed . ▁When ▁horses ▁are ▁removed , ▁signs ▁of ▁the ▁presence ▁of ▁various ▁mac rop ods , ▁specifically ▁the ▁black - fo oted ▁rock ▁wall aby , ▁increase . ▁Thus , ▁competition ▁with ▁horses ▁may ▁be ▁the ▁reason ▁for ▁the ▁decl ine ▁in ▁mac rop od ▁populations ▁in ▁certain ▁areas . ▁ ▁Br um by ▁populations ▁also ▁may ▁have ▁the ▁potential ▁to ▁pass ▁ex otic ▁dise ases , ▁such ▁as ▁equ ine ▁influen za ▁and ▁African ▁horse ▁sick ness ▁to ▁domestic ▁horses . ▁They ▁also ▁may ▁carry ▁tick ▁fe ver , ▁which ▁can ▁be ▁passed ▁to ▁both ▁horses ▁and