Birds’ Thermoregulation Helps Them Survive in Extreme Environments
The ability to regulate internal body temperature allows birds and mammals to thrive in both extreme cold and extreme heat, enabling them to settle almost anywhere on Earth.
Birds and mammals are the only endotherms, meaning they can regulate their body temperature internally. In contrast, all other animals rely on environmental temperatures to maintain a body temperature that supports normal activity. Homeostasis refers to the body’s ability to maintain internal balance through various systems and interactions among different organs, including the skin. Maintaining the proper internal temperature starts with “knowing” what that temperature should be, a process overseen by the hypothalamus in the front part of the brain. When a bird’s core temperature rises, the hypothalamus initiates cooling mechanisms such as panting and vasodilation. Exposed skin loses heat more easily than feather-covered skin, so some birds have bare, vascularized throat pouches that they flutter in the breeze to enhance heat dissipation.
When the internal temperature drops, the hypothalamus is stimulated and triggers heat conservation processes like vasoconstriction and fluffing feathers to trap air and keep it close to the skin for insulation. Behaviors to increase body temperature also include standing on one leg with the other leg tucked warmly into the feathers, and seeking fatty foods to provide additional energy.
The ideal body temperature for humans is 37°C. However, most birds maintain a higher body temperature, typically between 39°C and 40°C, regardless of their size or habitat. Birds in cold climates have thicker and denser feathers, and sometimes even feathered feet, as seen in larks flying at high altitudes in cold air. Birds swimming in cold water have highly waterproof feathers to keep their skin dry. In hot regions, birds cool down by evaporating water through panting and require readily available and reliable water sources to replenish lost moisture.
Birds enter a state of torpor when they are unable to maintain their body temperature.
For small hummingbirds living in mountainous areas, their high energy needs make it difficult to maintain a body temperature of 40°C during the cold nights when they can’t feed. Instead, they enter a state of torpor, reducing their energy needs to just 5% of their waking requirements. During torpor, their body temperature drops to about 18°C, and their heart rate and breathing slow dramatically. In this inactive state, hummingbirds can’t respond to threats, so they must choose the safest roosting spots before going into torpor.
Other bird species also experience torpor. However, no bird undergoes true hibernation like mammals, who remain dormant throughout the winter to survive months of scarce food. Birds prefer to migrate to more favorable climates as their winter survival strategy. Interestingly, while bats have flight abilities comparable to many migratory birds, their common winter strategy is hibernation rather than migration.
