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Toucans' bills act as radiators to regulate body temperature, researchers say

July 24, 2009 |  4:50 pm

Toco toucan

A longstanding mystery about toucans finally may be solved, thanks to a team of researchers who studied the birds and their giant bills.  The researchers, writing in the journal Science, say they've learned that the bills serve a unique purpose: They act as radiators to help the birds regulate body heat.

Until now, science has been unable to explain why toucans' bills are so large in relation to the rest of their bodies; the bill of one species, the toco toucan (above), typically accounts for about a third of its total body length.  Theories abounded, of course -- Charles Darwin suspected the large, colorful bills served to attract potential mates.  Other scientists have proposed that they evolved as a sort of warning to other animals to keep their distance or as a specialized fruit-peeling implement.

These theories may be part of the explanation for the evolution of the toucan's bill -- "The bill has many functions," study coauthor Denis Andrade told Science News -- but none of them represents the whole story.

National Geographic describes toucans' beaks as "a honeycomb of bone that actually contains a lot of air," but, it turns out, they also contain a network of blood vessels.  By controlling the amount of blood that flows to the uninsulated bill with its large surface area, the birds' bodies are able to determine how much heat escapes.

The research team, made up of scientists from Brock University in Ontario, Canada, and Universidade Estadual Paulista in Brazil, got an assist from modern technology in their study of a group of toco toucans. 

"We used infrared thermal imaging technology to assess the surface temperature of the bill of toucans while they were encountering a range of air temperatures from 10C to 35C," Glenn J. Tattersall of Brock University, who led the team, told the BBC.  "This allowed us to measure the exact temperature of the bill." An example of the imaging that resulted:

To test their reactions to changes in temperature, the team put each toucan in a temperature-controlled chamber and slowly raised the temperature over a six-hour period. Science News explains what happened next:

As the temperature increased, the birds’ bills warmed too, a change that the researchers interpret as a sign that the bird was flooding its beak vessels with extra blood. Yet the unfeathered skin around the birds’ eyes, an indicator of core body temperature, stayed about the same.

Toucans also spent a night in the chamber as researchers monitored bill temperature during sleep. When the birds settled down, their bills warmed up, suggesting they were dumping heat. Animals typically cool down as they fall asleep.

The discovery that the birds' bills help to regulate body temperature is significant not only in the study of the animals of today; it also "adds weight to the idea that some dinosaurs used large bony structures to regulate their temperatures," according to Discovery News.

Next up for the research team: studying other bird species to see if their bills act as radiators in the same way toucans' do.

-- Lindsay Barnett

Photo: Thiago Filadelpho / Associated Press
Video: wired via YouTube

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