How Animals Adapt Their Body Temperature to Survive Extreme Conditions

In 1774, Charles Blagden, a British physician-scientist, conducted an experiment that highlighted the ability of humans to maintain a stable body temperature, known as homeothermy, even in extreme heat. This phenomenon is common among mammals and birds, but recent research has revealed that many animals use a more flexible approach called heterothermy, where they vary their body temperature to adapt to environmental challenges.

Heterothermy allows animals to endure harsh conditions by adjusting their body temperature for varying durations. This adaptability is particularly evident in hibernation, where animals enter deep torpor, significantly reducing their metabolism and body temperature to survive cold winters. However, hibernation is just one form of heterothermy. Many mammals also use shorter bouts of shallow torpor, indicating that torpor serves multiple purposes beyond energy conservation during winter.

Comparative physiologist Fritz Geiser describes heterothermy as complex and fascinating. For instance, Australian eastern long-eared bats adjust their torpor based on weather conditions, using it more frequently during cold, windy, or rainy days. This strategy helps them conserve energy when flying becomes more demanding, and food is scarce. Similarly, pregnant hoary bats can enter torpor during spring storms, effectively pausing their pregnancies until conditions improve, which is beneficial for timing births when food is plentiful.

Other animals, like sugar gliders, rarely use torpor but can resort to it during severe weather events. During a storm with cyclone-force winds and heavy rain, sugar gliders were observed to enter torpor, significantly lowering their body temperature to conserve energy while staying safe in their nests. Similarly, a golden spiny mouse displayed multiday torpor during an accidental flooding event in a laboratory setting.

Heterothermy also serves as a defense mechanism against predators. The edible dormouse, for example, enters long periods of torpor during early summer, a time when owls are particularly active. By staying torpid in underground burrows, these small animals avoid becoming prey. Bats also adjust their torpor based on the moon's phase, spending more time in torpor during a full moon when they are more visible to predators.

In another example, the fat-tailed dunnart, a carnivorous marsupial, uses torpor as a survival strategy when it feels threatened by predators. Researchers found that dunnarts placed in enclosures with less ground cover, simulating a more exposed environment, were more likely to enter torpor, demonstrating the role of environmental factors in triggering this adaptive behavior.

Overall, the ability to control body temperature through heterothermy provides animals with a versatile tool to navigate a variety of environmental challenges, from extreme weather to predator threats, highlighting the remarkable adaptability of wildlife.