Too Much Sex and Too Little Sleep Can Kill These Endangered Marsupials

A study finds male northern quolls forgo rest to travel up to 6.5 miles in one night in search of a mate—the equivalent of a human walking 25 miles

a quoll on a branch
Northern quolls are the smallest of Australia's four quoll species. DEA / C.DANI / I.JESKE / Contributor via Getty Images

Male northern quolls in Australia are so focused on sex that they’re dropping dead from exhaustion, new research suggests. 

The small, spotted marsupials employ a mating strategy called semelparity, sometimes referred to as suicidal reproduction. This means the males only survive for one mating season, while females can live and breed for around four years. The practice isn’t unheard of: 19 marsupial species in the family Dasyuridae, which includes quolls, are semelparous. Pacific salmon die after spawning, and some octopuses self-destruct after laying eggs.

Smaller semelparous mammals ultimately perish from a flood of stress hormones after mating, writes Donna Lu for the Guardian. But male quolls show no signs of these hormonal changes at their time of death, so scientists didn’t know what causes their early demise. 

In a new study published in Royal Society Open Science, researchers attached miniature backpacks with trackers onto endangered northern quolls on Groote Eylandt, an island off the northeast coast of Northern Territory, Australia. They found a striking disparity in the amount of time males and females spent resting.

“During mating season, males are resting only around 7 percent of the day, which is very little, and they’re racing all over the place over long distances to find females to mate with,” co-author Christofer Clemente, a zoologist at the University of the Sunshine Coast in Australia, tells Stuart Layt of the Brisbane Times. “They also forgo grooming, they lose huge amounts of weight, they fight with each other, so they get lots of injuries.” 

But females rested more than three times as much—about 24 percent of the day.

Tracking data also revealed that some male quolls traveled shockingly far to look for mates. 

“Two males, who we named Moimoi and Cayless, moved for 10.4 kilometers [6.5 miles] and 9.4 kilometers [5.8 miles] in one night respectively,” lead author Joshua Gaschk tells the Australian Broadcasting Corporation’s Meg Bolton. “An equivalent human distance, based on average stride length, would be around 35 to 40 kilometers [22 to 25 miles].”

By the end of the breeding season, male quolls are usually in rough shape and an easy target for predators.

“They are balding, covered in scabs, sores, ticks and other parasites—it’s clear that their bodies are shutting down,” Jack Ashby, an expert on Australian mammals at the University of Cambridge in England who was not involved in the new study, tells NBC News’ Patrick Smith. “It certainly makes sense that the efforts that they put into finding mates during that period would lead to a lack of sleep and less time for looking after themselves generally, as this new study suggests.”

While this extreme method of breeding may not threaten a stable population, northern quolls are already endangered because of habitat loss and invasive species like cats, foxes and cane toads, per the Brisbane Times. Northern quolls were particularly affected by the invasion of the cane toads across northern Australia, which are highly toxic and kill quolls that attack or eat them. The Australian Wildlife Conservancy estimates the total remaining northern quoll population is around 100,000 but is “undergoing rapid decline.” 

Clemente tells the Brisbane Times that conservation efforts could be put in place around breeding season to help the animals move around and reproduce without getting hit by cars or eaten by predators.

Additionally, the new findings suggest quolls may be an ideal subject for further sleep research.

“If male quolls forgo sleep to the detriment of their survival, northern quolls become an excellent model species for the effects of sleep deprivation on body function,” Clemente tells the Brisbane Times.

Get the latest stories in your inbox every weekday.