Research has shown that one function is as a surface area for heat exchange. The bill has the ability to modify blood flow and so regulate heat distribution in the body, allowing it to use its bill as a thermal radiator. In terms of surface area used for this function, the bill relative to the bird's size is amongst the largest of any animal and has a network of superficial blood vessels supporting the thin horny sheath on the bill made of keratin called the rhamphotheca.