Animals Use Torpor to Hide From Predators & Survive Hard Times | Ars Technica

The ability to precisely regulate body temperature is often considered a hallmark of warm-blooded animals, but a growing body of research reveals a surprising degree of flexibility in how some species manage their internal heat. Beyond the familiar mechanisms of shivering and sweating, certain animals exhibit a remarkable capacity to enter states of controlled hypothermia – a phenomenon known as torpor – and even extend these periods for days, triggered by environmental stressors like floods or the threat of predation. This isn’t simply a passive response to conditions; it’s an active, physiological strategy for survival.

Torpor, in its most basic form, is a state of decreased physiological activity, characterized by reduced body temperature, slowed breathing and heart rate, and lowered metabolic rate. It’s a common adaptation among smaller mammals and birds, allowing them to conserve energy during periods of food scarcity or cold weather. However, recent studies are uncovering more nuanced and prolonged uses of torpor, challenging traditional understandings of how animals respond to environmental challenges.

Multiday Torpor: A Response to Unexpected Stressors

Researchers first documented this extended torpor in golden spiny mice (Acomys russatus) following an accidental flooding event in a laboratory setting. The mice exhibited a period of multiday torpor, with their body temperature dropping to around 75°F (24°C) and lasting more than seven times longer than typically observed for this desert rodent. This suggests that, at least in some species, torpor can be induced by acute, unexpected events beyond just seasonal changes. The research, published in the Australian Journal of Zoology, raises questions about whether this temperature reduction was a controlled entry into torpor or an uncontrolled drop due to heat loss (Geiser et al., 2018).

Ecophysiologist Julia Nowack of Liverpool John Moores University in England, a coauthor on a related study of sugar gliders, explains that this flexible use of torpor allows “heterotherms” – animals that can’t maintain a stable internal temperature – to “wait out a catastrophe.” Unlike “homeothermic” species, which maintain a constant body temperature, heterotherms can reduce their energy demands when faced with limited access to food or water, or even unfavorable temperatures. This ability to dial down metabolic processes can be crucial for surviving challenging conditions.

Predation Risk and Torpor: A Summer Snooze

The triggers for torpor aren’t always related to harsh environmental conditions. The edible dormouse provides a fascinating example of how predation risk can influence torpor patterns. Researchers were initially puzzled by the dormouse’s tendency to enter long periods of torpor during the summer months, when food is plentiful and temperatures are comfortable. However, further investigation revealed a correlation between torpor and the activity patterns of owls, a primary predator of the dormouse (Ruf et al., 2022).

By spending their nights torpid and hidden in underground burrows, the dormice effectively reduce their vulnerability to nocturnal owl attacks. This strategy highlights how torpor can be a proactive defense mechanism, allowing animals to avoid predation risk even when other resources are abundant. A similar strategy is observed in Fjelldal’s bats, which adjust their torpor use based on the lunar cycle, becoming more torpid as the moon grows fuller and they become more visible to predators (Nielsen et al., 2021).

The Role of Cover and Risk Assessment

The fat-tailed dunnart, a carnivorous marsupial native to Australia, further illustrates the link between perceived risk and torpor. A study examining dunnarts in different enclosure types demonstrated that animals in higher-risk environments – those with less ground cover – exhibited more variable body temperatures and foraged less frequently. This suggests that the dunnarts were actively reducing their activity levels and entering states of torpor to minimize their exposure to potential predators (McLean & Geiser, 2019). The presence or absence of protective cover directly influenced their physiological responses.

Understanding Heterothermy and Homeothermy

The contrasting strategies of heterothermic and homeothermic animals are central to understanding these behaviors. Homeotherms, like humans and many birds, expend significant energy to maintain a stable internal body temperature regardless of external conditions. This requires a constant intake of food and water. Heterotherms, allow their body temperature to fluctuate with the environment, reducing their metabolic demands during periods of stress. This flexibility provides a significant advantage in unpredictable environments.

While homeotherms can adapt to some degree, they lack the ability to drastically reduce their energy needs in the same way as heterotherms. This makes them more vulnerable to prolonged periods of resource scarcity or extreme conditions. The ability to enter torpor, particularly multiday torpor, can be a life-saving adaptation for heterothermic species facing unexpected challenges.

What Comes Next: Continued Research and Broader Implications

Further research is needed to fully understand the mechanisms underlying torpor induction and the factors that influence its duration and depth. Scientists are investigating the neurological and hormonal pathways involved in regulating torpor, as well as the genetic basis for this ability. Understanding these processes could have implications for a range of fields, from conservation biology to human medicine. For example, insights into the mechanisms of torpor could potentially inform strategies for preserving endangered species facing habitat loss or climate change. The ability to induce a state of controlled hypothermia could have applications in medical procedures, such as organ preservation or trauma care.

The ongoing exploration of animal thermoregulation continues to reveal the remarkable adaptability of life on Earth. These findings underscore the importance of considering the complex interplay between physiology, behavior, and environment when studying animal responses to environmental change. The seemingly simple act of “snoozing” through a difficult period can, in fact, be a sophisticated survival strategy honed over millennia.