Penguins get cold feet

Science in dialogue

Why don't penguins freeze their feet on the ice?

Penguins can reduce the blood flow to the feet and thus prevent them from losing too much heat. In winter, this keeps the penguin feet one to two degrees above freezing. On the one hand, little heat is lost and frostbite is avoided. On the other hand, the feet are so cold that the ice underneath does not thaw. And if it doesn't thaw, it can't freeze again, so your feet won't freeze. In order to keep the contact area as small as possible, the breeding penguins only touch the ice with their heels.

At the Frankfurt Zoo, we examine the thermoregulation in animals with a thermal camera, among other things. A color scale on the thermal camera makes the outside temperature of the body surface visible. In this case, blue indicates low temperatures and thus good thermal protection through insulation, red and white indicates heat loss, i.e. poor thermal insulation. The regulation of the penguin's foot temperature can also be measured in this way.

The penguin can control the blood flow to its feet by changing the diameter of the arteries. When it is cold, the blood flow is reduced to the minimum; when it is warm, on the other hand, it is increased. A sophisticated regulatory mechanism in the penguin's leg controls the flow of blood. The so-called counter-current heating principle warms the cold blood from the feet as it flows back into the body in the leg. Warm blood is transported through the artery to the foot; on the way there, the blood gives off heat to the returning veins. The cooled blood from the foot warms up on its way back into the body. The penguin does not cool down and can maintain its body temperature. If the animal gets too warm, it can switch off the exchange mechanism and regulate its body temperature via the heat leakage on the feet.

Penguins in arctic regions are exposed to constant cold. The dense, water-impermeable plumage and a thick layer of fat under the skin protect the animals' bodies from the cold. There are around 13 springs on every square centimeter of skin, which are attached like small roof tiles and keep wind and water out. In this way, penguins can avoid excessive heat loss and maintain their body temperature of 40 degrees Celsius. In addition, penguins move closer together. It is known that emperor penguins form groups of up to 50,000 animals. The warmed-up animals from the middle regularly replace those waiting at the edge. Without the group dynamics, a penguin alone would need twice as much energy in order not to freeze to death.

The question was answered by Dr. Dr. Sabine Hilsberg, research curator and veterinarian at the Frankfurt Zoo.