A project undertaken at the Institute for Land, Water and Society, Charles Sturt University and led by Melanie Massaro
In northern Australia, several ungulate species have established feral populations since their introduction in the early 1800s. Of those, three key species are common in Australia’s tropical savanna habitats: pigs (Sus scrofa), cattle (Bos taurus, B. indicus), and Asian water buffalo (Bubalus bubalis). As ungulates have high daily water requirements, they congregate close to water sources, such as rivers and waterholes. But these water sources are also critical refuges for the rich biodiversity of Australian savannas. For this study, we excluded feral ungulates from ephemeral waterholes by fencing 10 out of 20 waterholes in Limmen National Park. Since we erected fences in Sept 2017, we have completed 3 field seasons to measure how the exclusion of feral livestock from waterholes has changed water and soil quality, vegetation, bird diversity and macropod and dingo visitation.
Figure 1. Ephemeral waterholes, such as this one in Limmen National Park, provide water and habitat for many native bird and mammal species in Australian savannahs.
Figure 2. Due to their large size and the dry nature of their diet, feral ungulates such as these Asian water buffalos are highly reliant on water.
Exclusion fencing has had visible effects on vegetation. The exclusion of cattle and buffalos has resulted in continued vegetation changes in fenced study plots. Especially, two native pea species (Sesbania cannabina and Aeschynomenen indica) and wild rice (Oryza australiensis) are now prolific in the receding water zones of fenced sites. The pea species are also present at unfenced sites, but are heavily grazed by feral livestock. While we have not completed our analyses yet, these vegetation changes appear to have increased bird species richness (as measured through standardised searches of 30 minutes) at some fenced sites in 2020 compared to 2018. We are currently in the process of formally analysing these vegetation and bird diversity data to demonstrate those changes quantitatively since the exclusion of the feral ungulates.
In 2018 and 2019, we used motion-triggered cameras at fenced and unfenced waterholes to test whether native macropods preferentially visited savanna waterholes where large ungulates were excluded. We also investigated whether water scarcity affected herbivore activity 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 when cattle are present. Macropods and all ungulates visited waterholes more in 2019, a drought year, compared to an average rainfall year. Despite increasing prey activity, dingo presence at waterholes did not increase when water became scarce.
Surface water availability for savanna wildlife is likely to become less predictable and more restricted over the next few decades, as rising temperatures due to climate change are expected to increase evaporation in northern Australia. As we have shown in this study that feral livestock use ephemeral waterholes more frequently during dry periods when water availability becomes scarce, their impacts on water quality and damage to soils and vegetation increases severely, and thereby diminishes habitat for a range of native species. Hence, there is an urgent need to exclude feral livestock from ephemeral water sources in order to restore biodiversity refuges in savanna ecosystems in northern Australia.