Flaviemys purvisi
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ABC Science
By environment reporter Nick Kilvert
July 19, 2018
Cats haven't been considered a significant threat to the possums until now.
(Supplied: University of Melbourne)
Researchers have warned they may have underestimated the threat feral cats pose to the critically endangered Leadbeater's possum, after inadvertently capturing footage of a cat preying on possums as they attempt to leave a nesting box.
Ecologists from the University of Melbourne had motion-detecting cameras focussed on artificial nesting boxes as part of a study into nest-box microclimates in the Victorian Central Highlands.
But when researcher Leo McComb and his supervisor Dr Natalie Briscoe viewed the footage, they found a feral cat had visited the boxes on four occasions, once swiping at a possum as it attempted to leave.
Australian Mammalogy on Thursday, then "frantically went through all the other cameras" checking for images of cats, but didn't find any.
But a cat-trapping program in the area has since confirmed cats were preying on the possums.
"Seven cats [caught] in nine traps, put out over 2.5 kilometres; to catch seven in ten days, with two of them having Leadbeater's remains [in their stomachs], was a bit unexpected," Mr McComb said.
Cats have previously only been considered a peripheral threat to the possums, with the key threats being logging and severe fire.
But habitat destruction and an increase in feral animals don't occur in isolation, and the situation is likely to get worse as more of the Leadbeater's habitat is cut down, according to conservation and landscape ecology expert David Lindenmayer from ANU.
Key threats to the possums include fire and logging.
(Supplied
Feral cats and foxes have been shown to use roads to move into new habitat, and they are also known to be more effective at hunting in areas where canopy cover is reduced through logging or fire.
"The important thing to understand with feral animals is that they are often most effective in their hunting when there's another form of disturbance," Professor Lindenmayer said, who wasn't involved in the study.
"Really what's happening is that when humans disturb these landscapes, they create a conduit for these kinds of problems to occur and that's exactly what's going on."
Logging, habitat destruction opens the path for feral cats
Leadbeater's possums nest in tree hollows that form in large, old-growth trees.
For this reason, it can take hundreds of years for suitable habitat to develop.
But logging of mountain ash continues to reduce the range of the possum and availability of suitable habitat.
As well as killing animals directly through logging, reduced availability of tree hollows means the possums are becoming increasingly dependent on man-made nesting boxes.
The fear is that cats may learn to associate these nest boxes with food.
"There's only 1.16 per cent of the whole landscape that is old growth, and that's where you get the big trees which is what animals depend on," Professor Lindenmayer said.
"So when you start to concentrate animals around nest boxes you can run into really severe problems.
"I think this is some of the evidence now that's showing the kinds of problems we're dealing with."
While there has been some evidence of cats preying on Leadbeater's possums before, this is believed to be the first known instance of a cat directly targeting nesting boxes.
And while the footage is concerning, Dr Briscoe and Mr McComb stress more research and monitoring is needed before it can be confirmed this is an emerging threat.
"We wanted to raise that feral cats may be a new threat to the species that haven't been previously considered, although we're still unsure how big a threat because this is just one finding," Mr McComb said.
Leadbeater's nesting hollows can take hundreds of years to develop in old-growth forest.
(ABC News: Richard Willingham)
