Fire, cats and the Kimberley's declining mammals
A project undertaken at the Research Institute for the Environment and Livelihoods, Charles Darwin University, and supervised by Brett Murphy
Until just 20 years ago, the mammal fauna of northern Australia's vast savanna landscapes was considered secure; the catastrophic declines of central and southern Australia had not occurred in the north. However, work in Kakadu National Park since the 1990s has shown a massive, ongoing decline in mammal diversity and abundance. Recent evidence based on Indigenous knowledge has shown that these declines extend well beyond Kakadu, across the Top End of the Northern Territory. We are unable to implement an effective management response because the underlying drivers remain highly uncertain. Predation by cats and changes to fire regimes, and their interaction, have been strongly implicated, but it is unclear why northern mammals didn't decline earlier – cats were present for well over a century, and the cessation, or at least attenuation, of Aboriginal fire management occurred many decades ago.
The strongest evidence that fire also plays a role in the northern mammal decline is recent work from Kakadu, showing that between 2001 and 2007 mammal declines were greatest at the most frequently burnt sites. Similarly, results from CSIRO's Kapalga fire experiment suggested that a regime of annual fires reduced mammal abundance relative to unburnt controls. Critically, both of these studies have indicated that the predominant season of fire (i.e. early vs. late dry season) has little effect on small mammals – both early and late fires seem to be equally detrimental. This finding is starkly at odds with the prevailing fire management paradigm in northern Australia, that of extensive prescribed burning early in the dry season – under mild fire conditions – to prevent extensive, intense late dry season fires.
Prominent ecologists have advocated increasing the 'patchiness' and heterogeneity of fires to favour small mammals, despite little direct evidence linking them. Hence, one of the critical knowledge gaps is whether mammals are disadvantaged by some 'types' of fire. We expect that fire attributes associated with reduced shelter (e.g. high intensity, low patchiness) would facilitate predation by cats and be detrimental to mammals. This question is of enormous applied significance, because varying the frequency and intensity of fire through prescribed burning is one of the few tools available to land managers in these vast savanna landscapes.
Our study focusses on the remaining intact mammal assemblages in isolated parts of Australia's far northern savanna landscapes to examine the nexus between cats, fire and small mammals.
We will address four key questions:
Progress and Results
In 2015/2016, the project's fieldwork was completed. At 88 sites across Melville Island, which were surveyed for mammals in the early 2000s, we conducted live trapping of small mammals (5 nights trapping at each site) and camera trapping (5 cameras × 5 weeks observation at each site). We undertook detailed assessments of vegetation and habitat at these sites. We now have information on changes in small mammal distribution and abundance over a 15-year period, as well as the current distribution and abundance of feral animals (cats, cattle, horses) and dingoes.