Today, this ability to maintain a stable body temperature \u2014 called homeothermy \u2014 is known to exist among myriad species of mammals and birds. But there are also some notable exceptions. The body temperature of the fat-tailed dwarf lemur, for example, can fluctuate by nearly 45\u00b0F (25\u00b0C) over a single day.<\/p>\n
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In fact, a growing body of research suggests that many more animals than scientists once appreciated employ this flexible approach \u2014 heterothermy \u2014 varying their body temperature for minutes, hours or weeks at a time. This may help the animals to persist through all sorts of dangers.<\/p>\n
\u201cBecause we\u2019re homeotherms, we assume all mammals work the way we do,\u201d says Danielle Levesque<\/a>, a mammalian ecophysiologist at the University of Maine. But in recent years, as improvements in technology allowed researchers to more easily track small animals and their metabolisms in the wild, \u201cwe\u2019re starting to find a lot more weirdness,\u201d she says.<\/p>\n The most extreme \u2014 and well-known \u2014 form of heterothermy is classic hibernation<\/a>, which has been most extensively studied in critters who use it to save energy and so survive the long, cold winters of the Northern Hemisphere. These animals enter long periods of what scientists call deep torpor, when metabolism slows to a crawl and body temperature can drop to just above freezing.<\/p>\n \n The degree to which animals use heterothermy varies not just by species, but also between individuals. For example, greater hedgehog tenrecs (Setifer setosus) can maintain a higher, more stable body temperature during pregnancy \u2014 researchers believe this is important for fetal development. (Image credit: Courtesy Of Danielle Levesque)<\/p>\n But hibernation is just one end of what some scientists now consider a spectrum. Many mammals can deploy shorter bouts of shallow torpor \u2014 loosely defined as smaller reductions in metabolism and smaller fluctuations in body temperature \u2014 as the need arises, suggesting that torpor has more functions than scientists previously realized.<\/p>\n \u201cIt\u2019s extremely complicated,\u201d says comparative physiologist Fritz Geiser<\/a> of the University of New England in Australia. \u201cIt\u2019s much more interesting than homeothermy.\u201d<\/p>\n Australian eastern long-eared bats, for example, adjust their torpor use based on day-to-day changes in weather conditions. Mari Aas Fjelldal<\/a>, a bat biologist at the Norwegian University of Life Sciences and the University of Helsinki, used tiny transmitters to measure skin temperatures as 37 free-ranging bats in Australia went about their daily lives. Like many heterothermic species, the bats spent more time in torpor when it was cold, but they also sank into torpor<\/a> more often as rain and wind speeds picked up, Fjelldal and colleagues reported in Oecologia in 2021. This hunkering down makes sense, says Fjelldal: Wind and rain make flying more energetically demanding \u2014 a big problem when you weigh less than a small packet of M&M\u2019s \u2014 and make it more costly to find the insects the bats eat.<\/p>\n There are even reports of pregnant hoary bats entering torpor<\/a> during unpredictable spring storms, a physiological maneuver that basically pauses their pregnancies. \u201cIt means that they can, to some degree, actually decide a bit when to give birth,\u201d says Fjelldal, \u201cwhich is really handy when you\u2019re living in an environment that can be quite harsh in the spring.\u201d Fjelldal, who wasn\u2019t involved in that study, notes that producing milk is expensive metabolically, so it\u2019s advantageous to give birth when food availability is good.<\/p>\n You may like<\/p>\n \n Biologist Mari Aas Fjelldal studies torpor use in different bat species, including the brown long-eared bat (Plecotus auritus) she holds in this photo. (Image credit: Helene M. Hannestad)<\/p>\n Other animals, like sugar gliders \u2014 tiny, pink-nosed marsupials that \u201cfly\u201d through the trees using wing-like folds of skin \u2014 rarely use torpor but seem able to take advantage of it in the case of major weather emergencies. During a storm with category 1 cyclone winds of nearly 100 kilometers per hour and 9.5 centimeters of rain falling in a single night, the gliders were more likely to stay cuddled up in their tree-hole nests, and many entered torpor<\/a>, reducing body temperature from 94.1\u00b0F (34.5\u00b0C) to an average of about 66\u00b0F (19\u00b0C), Geiser and colleagues found.<\/p>\n Similarly, in response to an accidental flooding event in the lab, researchers observed a highly unusual period of multiday torpor<\/a> in a golden spiny mouse, its temperature reaching a low of about 75\u00b0F (24\u00b0C).<\/p>\n This more flexible use of torpor can help heterotherms wait out a catastrophe, Geiser says. In contrast, homeothermic species can\u2019t just dial back their need for food and water and may not be able to outlast challenging conditions.<\/p>\n \u201cMaybe there\u2019s no food, maybe no water, it may be really warm,\u201d says ecophysiologist Julia Nowack<\/a> of Liverpool John Moores University in England, a coauthor on the sugar glider study. Torpor, especially in the tropics, has \u201clots of different triggers.\u201d<\/p>\n 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<\/a> in early summer. At first, this behavior puzzled researchers \u2014 why snooze away the summer, when temperatures are comfortable and food abundant, especially if it meant forgoing the chance to reproduce?<\/p>\n \n Heterothermy evolved multiple times independently among mammals and birds, recent research suggests. Many of these creatures deploy torpor, wherein metabolism is reduced and body temperature becomes closer to ambient temperature. Such species include (clockwise from top left): Commerson\u2019s leaf-nosed bats, sugar gliders, fat-tailed dunnarts and fat-tailed dwarf lemurs. (Image credit: Credits Clockwise From Top Left: David Dennis, Deborah Metters, Sam Gordon, Nigel Voaden \/ iNATURALIST.ORG<\/a>)<\/p>\n 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<\/a>, safely hidden in underground burrows, to avoid becoming dinner. In what is thought to be a similar strategy to avoid nocturnal predators, Fjelldal\u2019s bats alter their torpor use<\/a> slightly depending on the phase of the moon, spending more time torpid as the moon grows fuller and they become easier to spot.<\/p>\n The fat-tailed dunnart<\/a>, 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.<\/p>\n Levesque, who has studied similar non-torpor temperature flexibility in large tree shrews, says that even small variations in body temperature can be important for saving water and energy.<\/p>\n Indeed, water loss during hot weather can pose serious risks to many mammals, and heterothermy is an important conservation tool for some. As Blagden observed, people are marvelously capable of maintaining stable temperatures even in horrifically hot environments, due in large part to our sweating abilities. But this isn\u2019t necessarily a good strategy for smaller mammals \u2014 such evaporative cooling in a sweltering climate can quickly lead to dehydration.<\/p>\n Instead, creatures like Madagascar\u2019s leaf-nosed bats<\/a> use torpor. On warm days, the bats enter mini bouts of torpor lasting just a few minutes. But during especially hot days, the bats become torpid for up to seven hours, reducing their metabolism to less than 25 percent of normal and allowing their body temperature to rise as high as 109.2\u00b0F (42.9\u00b0C). And in an experiment with ringtail possums<\/a>, slightly raising their body temperature by about 3\u00b0C (5.4\u00b0F) during a simulated heat wave saved the animals an estimated 10 grams of water per hour \u2014 a lot for a creature weighing less than 800 grams.<\/p>\n This heterothermic way of life gives some animals a bit of a buffer when it comes to coping with variability in their environments, says physiological ecologist Liam McGuire<\/a> of the University of Waterloo in Ontario, Canada. But it can only do so much, he says; heterothermy is unlikely to exempt them from the challenge of rapidly evolving weather conditions brought by climate change.<\/p>\n As for Blagden, he saw the human body as remarkable in its capacity to maintain a steady temperature, even by \u201cgenerating cold\u201d when ambient temperatures climbed too high. Today, however, scientists are beginning to appreciate that for many mammals, allowing body temperature to be a bit more flexible may be key to survival as well.<\/p>\n This article originally appeared in Knowable Magazine<\/a>, a nonprofit publication dedicated to making scientific knowledge accessible to all. Sign up for Knowable Magazine\u2019s newsletter<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"In 1774, British physician-scientist Charles Blagden received an unusual invitation from a fellow physician: to spend time in…\n","protected":false},"author":2,"featured_media":505881,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22],"tags":[49,48,295,66],"class_list":{"0":"post-505880","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-environment","8":"tag-ca","9":"tag-canada","10":"tag-environment","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/505880","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=505880"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/505880\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/505881"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=505880"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=505880"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=505880"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"A](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/02\/9cyi5AFbnQ89YSk273MH6V.png\")
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