The giant bill of the chestnut-mandibled toucan makes up a third of the bird's body length, but thanks to a honeycomb structure, it's not as heavy as it looks.

Scientists have long been baffled by the purpose of the toucan's most prominent characteristic. Is the oversized bill an advertisement for potential mates? An adaptation for fruit foraging? Or a warning for would-be predators? New research has found at least one practical function: temperature regulation. A network of blood vessels along the surface of the beak helps dissipate extra heat, and the vessels constrict when temperatures drop.