Similarly, in response to an accidental flooding event in the lab, researchers observed a highly unusual period of multiday torpor in a golden spiny mouse, its temperature reaching a low of about 75°F (24°C).
This more flexible use of torpor can help heterotherms wait out a catastrophe, Geiser says. In contrast, homeothermic species can’t just dial back their need for food and water and may not be able to outlast challenging conditions.
“Maybe there’s no food, maybe no water, it may be really warm,” says ecophysiologist Julia Nowack of Liverpool John Moores University in England, a coauthor on the sugar glider study. Torpor, especially in the tropics, has “lots of different triggers.”
Threats of a different sort, such as the presence of predators, can also prompt hunkering down. The (perhaps perfectly named) edible dormouse, for example, sometimes enters long periods of torpor in early summer. At first, this behavior puzzled researchers—why snooze away the summer, when temperatures are comfortable and food abundant, especially if it meant forgoing the chance to reproduce?
After looking at years of data collected by various scientists, a pair of researchers concluded that because spring and early summer are especially active periods for owls, these small snackable critters were likely opting to spend their nights torpid, safely hidden in underground burrows, to avoid becoming dinner. In what is thought to be a similar strategy to avoid nocturnal predators, Fjelldal’s bats alter their torpor use slightly depending on the phase of the moon, spending more time torpid as the moon grows fuller and they become easier to spot.
The fat-tailed dunnart, a mouse-like carnivorous marsupial native to Australia, is a third species to lie low when it feels more at risk of being eaten. In one study, researchers placed dunnarts in two types of enclosures: Some had lots of ground cover in the form of plastic sheeting, simulating an environment protected from predators, while other enclosures had little cover, simulating a greater risk of predation. In the higher-risk settings, the animals foraged less and their body temperatures became more variable.