Here’s what you’ll learn when you read this story:

• With only 150 or so individuals in the wild, the Gilbert’s potoroo is the rarest marsupial in the world.
• To help the species survive after translocation, scientists need to learn what fungi the potoroo eats.
• In a new study, scientists analyzed the feces of the “rat kangaroo,” along with other fungi-loving animals, to discern what habitats are best suited for transplantation.

The Land Down Under is the undisputed marsupial champion. Of the 334 species of marsupials—whose ancestors originally evolved on the North American continent during the Late Cretaceous—roughly two-thirds of them reside in Australia. But the rarest of the creatures within this group is the Gilbert’s potoroo. It’s one of only three extant species of potoroos in the world. Potoroos belong to the family Potoroidae, one of two families collectively known as “rat kangaroos.”

The Gilbert’s potoroo is so rare that only a few decades after its discovery by English naturalist John Gilbert in 1840, the species was believed to be extinct. It continued to be thought extinct for around a century, but amazingly, a small population of Gilbert’s potoroos was discovered living in 1994 at the Two Peoples Bay Nature Reserve in Western Australia. Since then, the Gilbert’s potoroo has lived on a knife’s edge. The species was nearly done in by a devastating brush fire that destroyed 90 percent of its habitat in 2015. Its tiny population has been slowly nursed back to roughly 150 individuals, but to build those numbers up any further, scientists to know more about one crucial detail—what it eats.

Scientists understand the broad outlines of the potoroo’s diet, and it’s a strange one indeed. Like the long-footed potoroo (Potorous longipes) and the long-nosed potoroo (Potorous tridactylus), which are classified as vulnerable and near-threatened, respectively, the Gilbert's potoroo’s diet consists of fungi—lots and lots of fungi. In fact, the small marsupial gets 90 percent of its calories from fungi. If the 2015 brush fire revealed anything, it’s that the species is too vulnerable to stay put in just one location, so scientists are trying to translocate some potoroos to create an insurance population. But for such a conservation effort to be successful, they need to bring the marsupial’s favorite grub with them.

In a new study published late last year in the journal Biodiversity and Conservation, a team of scientists led by experts at Edith Cowan University (ECU) in Joondalup, Australia, are closely examining the DNA in potoroo feces to understand what they’re eating. A technique known as metabarcoding can identify multiple species through samples of environmental DNA, or eDNA. Scientists used this technique to compare potoroo scat with feces belonging to other fungi-loving species, including quokkas (Setonix brachyurus), quendas (Isoodon fusciventer), and bush rats (Rattus fuscipes).

“One of the challenges was trying to determine what they are eating and where those resources can be found,” ECU Ph.D. student Rebecca Quah, lead author of the study, said in a press statement. “Mycophagous—or fungi-eating—mammal diets are quite hard to study because a lot of fungi remain undescribed. Habitat use between the quokka and potoroo were also really similar. Based on our results, we recommend focusing on areas where all three species persist together as an indicator of suitable food, or habitat, for future potoroo translocation sites.”

Translocation is vital for the small marsupial’s survival, especially since the tactic already saved the species once: after the 2015 brush fire, translocated populations lived on Bald Island and in a fenced enclosure at Waychinicup National Park. In late 2022, six Gilbert’s potoroos were released back into Two Peoples Bay National Park with GPS trackers and radio transmitters. However, fires—along with feral cats and foxes—remain a danger to the potoroo, so understanding everything about them, including their fungi-loving diet, will help secure their future for decades to come.

“Fungi-eating mammals are ecosystem engineers—they dig for fungi which helps in soil turnover, and they act as vectors for fungal spore dispersal,” Quah said in a press statement. “That is why it is vital that we do everything we can to help protect our native wildlife, and translocations are one important way to accomplish that goal.”