The bird famous as the mascot for Fruit Loops cereal, the Toco toucan (Ramphastos toco, since you asked) a native of South American rain forests, is the largest member of the toucan family. Its proboscis is ginormous. Researchers Glenn J. Tattersall, Denis V. Andrade, and Augusto S. Abe from Brock University, St. Catharines, Ontario, Canada, Universidade Estadual Paulista, São Paulo, Brazil, Instituto Nacional de Ciência e Tecnologia em Fisiologia Comparada, respectively, have joined forces under the auspices of a research grant at Brock University to study the Toco toucan's bill, and determine why it is so very large. Speculation about the reasons for the Toucans' bill size in the past has centered around the possibility of the bill as important for male display and mate-attraction, or as crucial for cracking nuts for food, but the Brock University researchers in their July article in Science magazine have a different theory.

The likelihood of the brightly colored bills being used by males to attract females is slim, given that females' bills aren't that different. The bills are much larger than they need to be, compared to those of other birds with similar diets. The Brock University researchers, under the leadership of Professor Tattersall, suggest that the bill is a heat-exchanger; that blood flowing through it is cooled. Their research suggests that the Toucan modifies blood flow and radiates the excess heat as a way of cooling down. The bird's bill can be as much as 25 centimeters long. Its efficacy as a cooling system is similar in efficiency and function to that of elephants' ears. Both are large, and thin, with a ready supply of blood that passes through and is cooled and re-circulated.

Researchers isolated a group of the toucans and then filmed their bills using stop-lapse photography and an infrared camera. As the birds got hotter, so did their bills, evidenced by their increased brightness in the photographs. As they cooled back down, blood flow to the many large blood vessels that are grouped around the beak's surfaces began to constrict, decreasing blood flow. During the course of a night, as the bird passes through different sleep-stages, their body temperature changes—as does the blood-flow to their bills. The scientists are now speculating that the bills of other bird species might serve a similar function.

The Science magazine abstract is here, with links to several video sequences of the infrared photographs. There's a short video excerpt linked below: