How Do Penguins Keep Their Bare Feet From Freezing?

A penguin may stand on ice while its body remains near the temperature of a human body. Yet its feet are not wrapped in thick feathers, and keeping them equally warm would waste enormous amounts of heat.

Penguins solve the problem partly by allowing their feet to become cold.

Warm blood traveling from the body toward each foot passes close to colder blood returning in the opposite direction. Heat moves from the outgoing blood into the returning blood before either reaches the body or the ice. This arrangement is called countercurrent heat exchange.

As a result, the blood reaching the feet has already surrendered much of its heat. The feet remain warm enough for living tissue to function, but they may be only slightly warmer than the surface beneath them. Because the temperature difference is small, relatively little heat escapes into the ice.

Meanwhile, the returning blood absorbs heat from the outgoing vessels before reentering the body. The penguin therefore recovers warmth that would otherwise be lost.

Blood flow can also be adjusted. When the bird needs to conserve heat, vessels restrict circulation near the surface. When it becomes too warm, increased blood flow through the feet and flippers can help release excess heat. Penguins may also rock backward onto their heels and tail or cover their feet with the lower part of the body.

The system does not make their feet completely immune to cold. It manages them as a cooler region that can safely operate at a temperature far below the body’s core.

A penguin stays warm not by heating every part equally, but by carefully deciding how much warmth its feet are allowed to receive.