A kangaroo, a possum and a bushrat walk into a burrow: research finds wombat homes are the supermarkets of the forest
First came a picture of an inquisitive red-necked wallaby, then an image of a bare-nosed wombat, followed by a couple of shots of the wombat’s burrow with nothing else in the frame.
By the time research scientist Grant Linley had looked through a further 746,670 images, he had seen 48 different species visiting the 28 wombat burrows that he had trained his cameras on.
Like a lineup of Aussie animals in a children’s book, Linley watched a parade of wallabies and kangaroos, lace monitors and possums, bush rats, button quails, echidnas and tiny marsupial antechinus hanging out at the burrows.
Some came to forage or take shelter, some to drink or bathe, and others to partake in a little geophagy (a technical way of saying “eating dirt”).
“The idea of [the burrows] being like an Airbnb or a supermarket isn’t a bad analogy of what we’ve observed,” says Linley, a PhD student at Charles Sturt University.
The cameras were set up across Woomargama national park and the neighbouring state forest, south of Wagga Wagga in rural New South Wales.
Less than 18 months earlier, the forest had been torched as six bushfire fires merged into a gigafire during Australia’s black summer of 2019 and 2020.
‘Like a 7/11 but they’re open all year round’
During the fires, claims swept across social media that wombats were actively shepherding animals into their burrows to escape the flames (if you think that sounds like the stuff of children’s literature, then you’d be right).
Prof Dale Nimmo, Linley’s supervisor, hosed those rumours down, but did describe wombats as “accidental heroes” in the fires. Small mammals are known to use the big, extensive burrows of wombats to hide out from fire.
But that gave Linley and Nimmo an idea. As the forest started to regrow, how important were the wombat burrows not just for the wombats themselves, but all the other animals living in the same habitat?
“They’re like a 7/11 but they’re open all year round, even after there’s been a fire and even after the wombats have stopped using them,” says Linley.
Nimmo, a fire ecologist at Charles Sturt University, says: “Some of the animals are probably using the burrows opportunistically. There’s a shelter and they can sleep there and be protected from predators. So they’re a refuge. For other species, it’s a place where they will find food, so it’s like a supermarket.”
Linley’s research, just published in the international Journal of Mammalogy, compared activity around 28 wombat burrows with areas of the forest close by that didn’t have a burrow.
The research, funded by WWF Australia, found the burrows were hotspots for animals and were likely helping the animals survive and recover from the fires. They were especially important for small mammals.
In a charred landscape, there are fewer places for small animals to hide out from predators and particularly from feral cats. The burrows provided shelter.
“After fires, when there’s high vulnerability to predators, the burrows can act like as that refuge while they eke out a recovery,” says Nimmo.
It’s possible, the research says, that smaller mammals like hanging around burrows because the burly wombats “actively deter larger competitors” from the area around their homes.
When it rained, the cameras saw parts of the burrows and entrances filled with water, creating a place for birds and mammals to bathe and drink.
The mounds of disturbed soil also seemed to attract species, with one wallaby seen clearly in one burst of images eating the soil.
The ramifications of wombats in decline
In Australia’s eastern forests, the wombat is unique in its ability to dig “wide, deep and elaborate” burrows, the research says.
While the common bare-nosed wombat is not considered threatened, its range has been dramatically reduced since European invasion. The common wombat’s relatives, the southern and northern hairy-nosed wombat, are considered threatened.
Climate change is predicted to even further reduce the places wombats can live, while at the same time the risk of more frequent and severe bushfires – which wombats help some animals survive – is rising.
“Australia has lost so many digging and burrowing mammals since colonisation – bilbies have declined by 80%,” says Nimmo.
“If [wombats] do decline and become locally extinct then we now know that their burrows will persist for a while, but then degrade, and would have real ramifications for a whole lot of other species.”
Back at Grant Linley’s desk, the researcher recalls the “shock” he felt at opening the memory cards of the cameras and realising the monotony of having to look at more than 700,000 images.
He opened the first image in December 2021 and finished in October the following year.
“After [I’d] done the first SD card, and there’s 350,000 on that, I knew what was coming. I was doing it anywhere and everywhere. Mostly at my desk, but sometimes on planes, at airports and on holiday. I had to get this done.
“What kept me going was the thought that the next burst of images could have something interesting on it. I was really hoping to see a spotted quoll.”
He didn’t.