The Kangaroo Island dunnart (Sminthopsis aitkeni) is a small insectivorous marsupial found only on the western end of Australia’s third largest island, Kangaroo Island (KI) off the coast of South Australia.
After extensive wildfires in late 2019 and early 2020 scorched 98% of the species’ remaining habitat, it has been classified as critically endangered – it’s estimated there are only about 500 dunnarts left within this restricted geographical area.
Now, scientists have found that dunnarts face the threat of extinction by feral cats.
Evidence of eight dunnarts in the digestive tracts of seven feral cats has been uncovered, confirming for the first time that feral cats do predate on KI dunnart and that they were efficient hunters of the species directly after the fires.
The new study has been published in Scientific Reports.
Because there are so few dunnarts restricted to a small, fragmented geographical area, they are exceptionally vulnerable to stochastic events (unpredictable events that can affect population and community dynamics, like bushfires and predation from introduced species) that could lead to their extinction.
“Efforts to provide immediate relief from an invasive predator, including the provision of refuge, is critical, and can mean the difference between survival and extinction,” the authors say.
Controlling feral cats following the 2019 bushfires
Feral cats hitched a ride with European colonisers to the continent in the late 1700s, and have since contributed to the mass extinctions of numerous species of smaller native fauna.
Their effect is particularly acute on islands – cat predation has contributed to more than 13% of globally recorded extinction events.
Because it hadn’t yet been confirmed whether feral cats were also a threat to Kangaroo Island dunnarts, researchers from the University of Adelaide and Nanyang Technological University in Singapore set about finding out.
Immediately following the 2019 bushfire, feral cats on KI were captured as part of the national feral cat control program and humanely euthanised in accordance with South Australia animal welfare laws.
“The control of feral cats was seen as a priority to reduce the pressure they might put on the wildlife in those places,” says senior author Dr Louis Lignereux, from the School of Animal and Veterinary Science at the University of Adelaide.
“Not only pressure on the dunnarts, but also on the pigmy possum, the southern brown bandicoot, and many more species, including birds and reptiles,” he adds. “They all just suffered the loss of a large part of their habitat.”
The cats were caught from two areas: a 12ha unburnt patch at the Western River Refuge and a 420ha completely unburnt patch of vegetation at the North-West Conservation Alliance within the De Mole River Catchment.
First author Pat Hodgens of Terrain Ecology and the organisation played an important role in feral cat control and data collection for this research, and led the construction of a feral predator-free safe haven within the Western River Refuge to protect the KI Dunnart.
Feral cat populations need to be controlled
“Through this cat control, we had the possibility to access the gastrointestinal tract contents of 86 cats, which we analysed,” explains Lignereux. “The gastrointestinal tract content represents what the cat has eaten in the previous 26-35 hours.”
8.1% of sampled cats had evidence of KI dunnarts in their stomachs, suggesting that they are efficient hunters of the small numbers of dunnarts that remain following the bushfires.
This finding raises concerns for the survival of the species in places where the feral cats are not controlled and has implications for future KI dunnart conservation measures – like the need to survey the KI dunnart both in those places that were left unburnt, but also where the KI dunnart was thought to live before the fires.
“The first implication is of course to protect the remaining KI dunnarts in those unburnt patches by increasing the efforts to control the feral cats and building cat-proof fences to avoid reinfestation once the cat has been controlled,” says Lignereux.
“Outside Kangaroo Island, the feral cats are a threat to multiple wildlife species. With our study, we would like to emphasise the need to control those cat populations,” he adds.
“More broadly, through our study, we would like to showcase the dramatic effects of the succession of anthropogenic stochastic events and invite the readers to reflect on biodiversity preservation.”
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