The impacts of feral ungulates on ephemeral savanna waterholes in the Northern Territory and their flow-on effects for native wildlife

Helenna Mihailou

Research output: ThesisDoctoral Thesis

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Globally, savannas have been severely degraded through their conversion to pastureland for domesticated ungulate species. Grazing pressure from ungulates has negative impacts on native savanna flora and fauna species, particularly in areas where large herbivores have been absent for long periods, such as in northern Australia. Over the last ~200 years, several ungulate species have been introduced to northern Australia and have established large feral populations, including cattle (Bos taurus, B. indicus), Asian water buffalo (Bubalus bubalis), and pigs (Sus scrofa). These species have high water requirements and thus, congregate around water points. Water is a limited resource in savannas, particularly during periods of seasonal and interannual water scarcity. Hence, many native species also rely on savanna waterholes, which provide habitat, food, and water resources. However, it is largely unknown how periods of water scarcity affect feral ungulate behaviour around waterpoints and what flow-on effects this has on native flora and fauna communities in Australian savannas. In this study, I investigate these knowledge gaps using an ungulate exclusion experiment at ephemeral savanna waterholes in Limmen National Park, Australia.

To investigate how water scarcity affects feral ungulate use of waterpoints, I studied changes in the seasonal and interannual visitation behaviours of feral cattle, water buffalo, and pigs at savanna waterholes. All three species visited waterholes more often, for longer periods, and in larger numbers during a drought year, compared to an average rainfall year. Cattle considerably increased their use of waterholes as the dry season progressed, while buffalo did not change their waterhole use. Pig visitation to waterholes only increased when water scarcity was most extreme at the end of the dry season during the drought.

In African savannas, large herbivores can competitively exclude smaller species from accessing water. Yet, no studies have investigated whether the presence of large feral ungulates at waterholes affects the behaviour of smaller native herbivores in Australia. I found that macropods avoided waterholes when cattle presence was high but did not preferentially use waterholes where ungulates were excluded. The potential for competition between feral and native herbivores is exacerbated by water scarcity.

Australian savannas support a rich diversity of birds, which rely on waterholes for drinking and bathing, particularly when water is scarce. Ungulates aggregate around waterholes, but few Australian studies have investigated how this impacts native plant and bird communities in water limited savannas. I found that ungulate presence affected vegetation recovery during a drought and bird diversity was significantly lower as the dry season progressed.

Overall, this study demonstrates that even highly mobile fauna, such as macropods and birds, suffer negative impacts from ungulate activity around waterpoints, particularly during water scarcity events. Vegetation communities closest to water are the most vulnerable and are damaged even at very low ungulate densities. The use of fencing to exclude ungulates from small, but resource rich areas in Australian savannas provides important refugia sites for native fauna. Collectively, we must find practical, scientifically informed solutions to control feral ungulate species before vulnerable native species are lost.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
  • Massaro, Melanie, Principal Supervisor
  • Nimmo, Dale, Co-Supervisor
Place of PublicationAustralia
Publication statusPublished - 2022


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