Animals That Control Their Body Heat: Beyond Warm-Bloodedness
The animal kingdom continues to surprise, and recent research is revealing a far more nuanced picture of how creatures regulate their body temperature than previously understood. For decades, the assumption was that mammals and birds largely adhered to a standard of maintaining a stable internal temperature – a process called homeothermy. But a growing body of evidence suggests that many more species employ a flexible approach, varying their temperature for minutes, hours, or even weeks at a time. This adaptability, known as heterothermy, appears to be far more widespread than scientists once believed, offering a potential key to survival in challenging environments.
The story begins surprisingly far back, with British physician-scientist Charles Blagden’s self-experimentation in 1774. He willingly subjected himself to temperatures exceeding 200°F (about 93°C), noting with fascination that his own body temperature remained remarkably stable at approximately 98°F (37°C). This capacity for thermal regulation, once considered exceptional, is now being recognized as a spectrum of abilities across the animal world.
Beyond Hibernation: A Spectrum of Thermal Flexibility
Even as hibernation – the prolonged state of reduced metabolic activity seen in animals like bears during winter – remains the most well-known example of heterothermy, it represents just one conclude of the scale. Researchers are discovering that many mammals utilize shorter, shallower bouts of torpor, reducing metabolism and fluctuating body temperature as needed. This isn’t simply about surviving the cold; it’s about conserving energy and adapting to a range of environmental pressures.
Danielle Levesque, a mammalian ecophysiologist at the University of Maine, explains that advancements in technology have been crucial to these discoveries. “Because we’re homeotherms, we assume all mammals work the way we do,” she says. “But in recent years, as improvements in technology allowed researchers to more easily track modest animals and their metabolisms in the wild, ‘we’re starting to identify a lot more weirdness.’” Levesque’s work focuses on understanding the physiological mechanisms underlying these variations.
The benefits of this flexibility are becoming clearer. Australian eastern long-eared bats, for instance, adjust their torpor apply based on daily weather changes. Research led by Mari Aas Fjelldal at the Norwegian University of Life Sciences and the University of Helsinki revealed that these bats enter torpor more frequently during periods of wind and rain. As reported in Oecologia in 2021, this behavior makes sense given that flying becomes more energetically demanding in inclement weather, especially for such small creatures.
Torpor as a Survival Strategy
The use of torpor isn’t limited to avoiding harsh weather. Researchers have even observed pregnant hoary bats entering torpor during unpredictable spring storms, effectively pausing their pregnancies until conditions improve. This allows them to conserve energy and time their births to coincide with periods of greater food availability. Fjelldal, who wasn’t involved in that study, notes that producing milk is metabolically expensive, making optimal timing crucial.
Even the edible dormouse exhibits a surprising strategy, entering extended periods of torpor during the summer months to avoid predation by owls. This behavior, discovered through years of data collection, suggests that these small mammals are proactively minimizing their risk of becoming a meal.
Water Conservation and Climate Change
Beyond predator avoidance, heterothermy plays a crucial role in water conservation, particularly for smaller mammals in hot climates. While humans rely on sweating to regulate temperature, this can quickly lead to dehydration in smaller species. Animals like Madagascar’s leaf-nosed bats utilize brief bouts of torpor to reduce metabolic rate and minimize water loss. Similarly, research on ringtail possums demonstrated that slightly elevating their body temperature during a simulated heatwave saved them a significant amount of water – approximately 10 grams per hour.
Liam McGuire of the University of Waterloo emphasizes that this thermal flexibility provides a buffer against environmental variability, but it’s not a foolproof solution. Heterothermy is unlikely to fully protect animals from the escalating challenges posed by climate change.
As our understanding of these remarkable adaptations grows, it becomes increasingly clear that the animal kingdom is far more resourceful and resilient than previously imagined. The “weirdness” Danielle Levesque refers to isn’t simply a curiosity; it’s a testament to the power of evolution and the diverse strategies life employs to thrive in a changing world. Further research, including long-term monitoring and detailed physiological studies, will be essential to fully unravel the complexities of heterothermy and its implications for conservation in a warming world.
This article originally appeared in Knowable Magazine, a nonprofit publication dedicated to making scientific knowledge accessible to all. Sign up for Knowable Magazine’s newsletter.