Giant Toucan Bills Help Birds Keep Their Cool
for National Geographic News
|July 23, 2009|
Good for more than sniffing out Froot Loops, the toucan's big bill also helps the bird dump heat when its body gets too warm, a new study says.
The discovery may even lead to clues to how some dinosaurs did the same.
For over a century biologists have puzzled over why toucans have such monstrous and colorful bills. Darwin theorized that they attracted mates. Others have suggested the bills are fruit peelers, territorial weapons, and visual warnings to predators.
Glenn Tattersall at Brock University in Canada and a team of colleagues wondered if perhaps the beak served an altogether different purpose.
Like any warm-blooded animal, the toucan has to release excess body heat—humans do it in part by sweating; dogs by panting.
The researchers figured that the "large uninsulated appendage," with its extensive network of blood vessels close to the surface, "might be an important tool for helping toucans cool off," Tattersall said.
To find out, the team regularly photographed captive toucans with infrared cameras, which display warm areas as bright and cool regions as dark.
In hot conditions, the toucans' bills appeared to glow with radiated heat as warm blood flooded them. At cooler temperatures, the bills would go dark—blood flow to the bills had effectively stopped.
It's unclear whether many other bird species use their bills to shed heat, said study co-author Denis Andrade of São Paulo State University in Brazil.
Ducks and geese "seem to be able to do the same thing, although not to the same extent as toucans," he said.
Previous studies have also suggested that some dinosaurs were blessed with similar natural radiators on their bodies.
Debate has been ongoing about the function of Triceratops' head frills (Triceratops pictures) and Stegosaurus' plates (Stegosaurus picture), for example, with some experts suggesting uses as varied as cooling, defense, courtship displays, or even interspecies ID.
(Related: "Stegosaur Plates Used for ID, Not Defense, Study Says.")
To strengthen the case for frills and plates as cooling mechanisms, researchers would need to prove that these dinosaurs could control blood flow to their bony ornaments, study leader Tattersall said—something top paleontologists have tried and, so far, been unable to do.
Paleontologist Kevin Padian at the University of California, Berkeley, agreed, adding that "most accessory [temperature control] by vertebrates, from lizards to elephants, is behavioral: The antelope turns towards or away from the sun to thermoregulate, just as we do.
But "without being able to observe directly those extinct dinosaurs, we can't assess how they might have used their regular bodies, let alone their bizarre structures, for thermoregulation."
Findings to be published tomorrow in the journal Science.
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