Relative to its body size, the huge beak of the toco toucan is the largest of any bird. It allows the toucan to eat both fruit and small animals, and display to both mates and rivals. Darwin himself speculated that it acts as a billboard, shaped by sexual selection to display bright colours that could be attractive to potential mates. But the toucan’s bill has another function that has only been discovered. Like the ears of an elephant, the toucan’s bill is a radiator.
It certainly has all the characteristics of a biological radiator. It’s big and has a surface area that’s 25-40 times larger than normal for a bird of its size; in fact, the bill accounts for 30-50% of the bird’s total surface area. It also lacks any insulating layer of fat, feathers or fur, and beneath its horny exterior, lies a rich network of blood vessels.
These vessels are the means through which the toucan exchanges heat. When it’s warm, it widens the vessels and allows the heat of its blood to radiate into the atmosphere. When it’s too cold, it limits the loss of heat by shutting down the blood flow to its bill.