Feral ungulate and macropod responses to resource scarcity and predation risk at savanna waterholes

When exotic species are introduced to new environments, they often have a competitive advantage over native species. In northern Australia, pigs, cattle, and water buffalo have established widespread, feral populations. As ungulates have high water requirements, they typically congregate near waterpoints. We used a fencing experiment to test whether native macropods preferentially visited savanna waterholes where large ungulates were excluded. We also investigated whether water scarcity affected the visitation behaviour and temporal activity patterns of herbivores at waterholes and whether increasing prey aggregation at waterholes increased dingo presence. We found that macropods did not use fenced waterholes preferentially over unfenced ones. Cattle presence at waterholes increased as water became scarce, while macropod and pig presence peaked in the middle of the dry season. Macropod activity declined rapidly at the end of the dry season when cattle activity was greatest, suggesting that macropods may avoid waterholes in areas utilised by cattle when competition for resources is high. Macropods and all ungulates visited waterholes more during a drought year compared to an average rainfall year. Despite increasing prey activity, dingo presence at waterholes did not increase when water became scarce. However, dingo presence increased significantly on moonless nights. Our results suggest that competition between macropods and ungulates may intensify during periods of water scarcity. Climate change and pastoral intensification are likely to increase competition for resources between ungulates and macropods in Australian savannas, potentially threatening macropod populations across the landscape in the future. Significance statement: In northern Australia, feral populations of pigs, cattle, and water buffalo compete with native wildlife for access to water sources. As interspecific competition favours species with a size advantage, we tested whether kangaroos and wallabies (macropods) preferentially use waterholes where large ungulates (cattle and buffalo) were excluded. We found that macropods avoided waterholes when cattle presence was high but did not preferentially use waterholes where livestock were excluded. When water scarcity peaked during a drought, macropods and all three feral ungulate species visited waterholes more. However, increased prey presence at waterholes during the drought did not correspond with increased predator (dingo) presence. Our study advances the understanding of behavioural interactions between invasive and native species at important shared resources, and how this may affect wildlife conservation in an increasingly unpredictable environment.