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Few mammals sleep as deeply as the ampurta. When the blonde, rat-like marsupial returns to its burrow after a night of hunting in the Australian desert, it drifts into a slumber known as torpor. While many other mammals quickly burn through their energy reserves in order to maintain stable body temperatures as they fall asleep, ampurtas allow their bodies to cool down to as low as 50 degrees Fahrenheit, saving energy critical to survival in this harsh desert environment.
“I’ve held some when they’re in torpor, and they feel like they’ve been in a freezer,” says wildlife ecologist Dympna Cullen of the University of New South Wales in Sydney. Instead of using their own energy to warm up again, upon waking, the animals drag themselves to the mouths of their burrows to soak up the morning sun.
Some scientists say this energy-saving trick helped the ampurta—once thought doomed to extinction—to make a comeback during a severe drought. In what they call a “rare and hopeful conservation signal,” the authors document in a new study in Biological Conservation how, during a two-year drought that lasted from 2017 to 2019—one of the region’s harshest droughts on record—the vulnerable marsupials actually significantly extended their range, reclaiming a large chunk of lost habitat. “Everything crashes during a drought,” Cullen says, “so it was quite unexpected that not only were [ampurtas] increasing in abundance but also increasing their area of occupancy by quite a significant amount during a drought.”
“I’ve held some when they’re in torpor and they feel like they’ve been in a freezer.”
Like many other Australian mammals, the ampurta—the Aboriginal name for Dasycercus hillieri or the crest-tailed mulgara—once seemed like it might vanish from the Earth. Rabbits brought to Australia by European colonists in the 19th century wreaked ecological havoc on the continent. They ravaged Australia’s vegetation, robbing small native herbivores of cover and food, including some of the ampurta’s prey, such as smaller mammals. The rabbit boom also fed the spread of non-native foxes and cats, which picked off ampurtas and other native wildlife. But in 1996, the Australian government released a rabbit-killing virus to quash rabbit populations, which allowed some native species populations to recover. Ampurtas were downgraded from endangered in the mid-1990s to “vulnerable” in 2013, and eventually to a species of “least concern.”
Starting in 2015, Cullen’s colleagues documented more and more ampurta tracks, scats, and burrows in central Australia’s Strzelecki Desert, especially in a study area there called Wild Deserts. The project was part of Cullen’s Ph.D. research. When she and the team tallied their results, they found that by 2021, ampurtas had actually increased their range by 19,000 square miles, an area larger than Denmark. And this was in addition to the roughly 52,000 square mile-sized area the marsupials had already reclaimed since the mid-1990s. Remarkably, ampurtas have even managed to cross the dingo barrier fence, erected to keep wild dogs called dingoes out of the southeastern state of New South Wales. On the far side of that fence, because dingoes are scarce, cats and foxes—the ampurtas’ main predators—run rampant.
Cullen attributes the ampurta’s drought resilience to several factors—not just its deep cooling slumber, but also its flexible diet. Ampurtas eat everything from invertebrates to reptiles and small mammals. And unlike many other mammals whose ability to mate and give birth to young typically takes a hit under harsh environmental conditions, ampurtas kept producing full litters of up to eight young even during the drought. Though that isn’t always a beneficial strategy, as it can mean wasting energy on offspring that will die under harsh conditions, it seems to have worked out well for ampurtas. Being able to reduce their energy requirements by 10-40 percent through torpor must have helped with this, by allowing females to put on weight prior to breeding to buffer the physical toll of reproducing. “This torpor seems to be their key adaptation,” Cullen says.
The results underscore that, if threats like non-native species are controlled, some desert-adapted creatures like the ampurta can persevere in severe climate conditions. Indeed, one 2016 study found that other Australian species, such as the dusky-hopping mouse and the plains mouse, have recently bounced back after rabbit populations were reduced, in spite of near-drought conditions. Cullen hopes that some of the ampurta’s close relatives that have similar adaptations, such as western quolls, a near-threatened spotted marsupial, will also persevere under drought conditions.
But it’s unclear how far the ampurta’s drought adaptations will take them as the planet continues to warm. If nights become warmer, ampurtas might not be able to cool down their bodies as effectively. When Cullen and her colleagues used computer models to project the ampurtas’ suitable habitat decades into the future, they observed severe declines, especially under maximum warming scenarios.
Regardless, the study is a rare piece of good news, especially on a continent which has seen 35 percent of the world’s mammal extinctions, with another 52 species on the brink. “It’s really rare in Australia to see a mammal recovering like this full stop,” Cullen says, “but to this scale is quite remarkable.” 
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Lead image: Joseph Smit, Proceedings of the Zoological Society of London
