A project undertaken at the Conservation Ecology Centre, Victoria, and supervised by Dr Jack Pascoe.
In Australia, inappropriate fire regimes and introduced predators are the primary drivers of post-European mammal extinctions. In particular, mammals that dwell or forage on the ground and weigh between 35 g to 5.5 kg, the “critical weight range”, are the most at risk of extinction. Species with these traits are often selected for and accessible to introduced predators such as feral cats and foxes. Unfortunately, a growing body of evidence suggests the threatening processes of invasive predators and inappropriate fire regimes may interact, compounding threats to native fauna. For example, fire may increase the vulnerability of native mammals to foxes and feral cats by removing dense understorey vegetation, and predators may increase their activity in recently-burnt areas.
Example of Long-nosed Potoroos displaying strong site fidelity post fire. Pre-fire home range = dotted line, and post-fire home range = solid line.
Whilst the potential consequences of these interacting threats are high, there is much we don’t understand about how fire alters predator-prey dynamics. There is often little detailed information available describing the movement behaviours of ground-dwelling mammals before fire, and almost no information known about how these behaviours change in the immediate aftermath of a fire. To date, financial, logistical and weight constraints have limited the application of GPS technology in this context; however, recent advances have resulted in the production of GPS collars that are increasingly lighter, cheaper, and more powerful.
Pre-fire home ranges of all collared Long-nosed Potoroos (2020 – 23)
One such species that may be particularly sensitive to the impacts of fire is the Long-nosed Potoroo (hereafter ‘LNP’). This digging native mammal fulfills a vital functional role within ecosystems through the turnover of soil and dispersal of mycorrhizal fungi. Weighing between 600 – 1600 g, this species is also at high risk of predation by introduced predators. The Heathy Woodlands of the Carlisle Heath in south-west Victoria continues to support robust populations of LNP’s, however a series of recent summer wildfires that threatened local communities have resulted in an increased focus on reducing the fuel hazard in this region.
Example output of Hidden Markov Modelling
With the generous support of the Hermon Slade Foundation, we aimed to intimately describe the movement ecology of LNPs before, during and after fire in the Carlisle Heath using GPS collars. This project has substantially improved our understanding of Long-nosed Potoroo ecology and the impact fires and invasive predators have on their populations in the region.
Our project is the first to trial the use of circular cable-ties to attach GPS collars on LNPs. To date, beyond some minor hair loss, we have observed no significant welfare issues using this approach and have been able to quickly attach GPS collars to conscious individuals in the field. This approach has negated the need to sedate or transport animals elsewhere for collar attachment.
Additionally, the GPS data we collected suggests that potoroos have home range areas of approximately 6 – 13 hectares, somewhat larger than estimates produced using other approaches (e.g. trapping or VHF tracking) in the past. Moreover, our data suggests there is little evidence of territoriality in this species. Collared animals were active during both the day and the evening, contrasting with the traditional assumption that this species is primarily nocturnal. We have also determined that potoroos have several frequently used resting sites within their range – often within the thick skirts of the Austral grasstree (Xanthorrhoea australis).
Unfortunately, we have repeatedly demonstrated that the mortality of potoroos post-fire is very high – approximately 80% of collared animals succumbed to predation in the first few weeks post-fire. There is little evidence that the fire itself resulted in any mortality, with animals able to seek nearby shelter in unburnt areas when the fire was active. In contrast, there is strong evidence that foxes may be responsible for several mortality events, with several collared LNPs found buried underground – a characteristic fox behaviour. The GPS data generated by the collars have been instrumental in helping us understand why this might be happening. Potoroos displayed strong site fidelity regardless of how much of their home ranges burnt. This behaviour often resulted in potoroos spending extended periods either within the burn scar itself or along burn edges – areas that are also likely to be selected by invasive predators who exploit burn scars.