David L. Shenkenberg, email@example.com
SÃO PAULO, Brazil – The 18th-century French naturalist Buffon called the colorful, long, hard and curved appendage “grossly monstrous” a century before Charles Darwin wrote that it could be a sexual ornament. Now, thanks to an infrared video camera, researchers have discovered that the toucan’s bill acts as a heat sink.
“I’ve felt baby toucans, and you can feel the heat on the bill. That was the first indicator [that the bill acts as a heat sink],” said Glenn Tattersall, the professor from Brock University in Saint Catharines, Ontario, Canada, who led the study.
An infrared camera revealed that the toucan uses its bill as a heat sink. Courtesy of Glenn Tattersall.
“All birds have a similar capacity [to regulate blood flow to control temperature] that I’ve seen. It has been looked at in ducks and geese,” Tattersall added. The rhea, a large flightless bird, can transfer blood flow from foot to foot. Humans also have more blood vessel anastomoses, or connections, in their extremities, which is why more heat is lost from the extremities.
The investigators also suspected that the toucan might use its bill for temperature regulation because it is enlarged, uninsulated and contains a network of blood vessels. To control heat exchange, blood flow must be adjustable. However, it was not known whether the toucan regulates the blood flow in its bill. “[Temperature control] is a nice analogy for understanding engineering principles,” Tattersall said.
He did the study in Brazil with colleagues at Universidade Estadual Paulista. The researchers studied the toco toucan (Ramphastos toco) because, out of all toucans, it has the largest bill. They looked at a total of six birds, four adults and two juveniles. The birds were kept in an outdoor aviary until it was time for the experiment, at which point they were placed one at a time in a temperature-regulated chamber heated to between 10 and 35 °C.
The researchers viewed the toucan with an infrared video camera: Model 7515 from Mikron Instruments. The camera’s standard software was used to take temperature measurements of specific areas on the body and bill of each toucan.
Courtesy of Thiago Filadelpho.
“My camera is five years old. It constrained our ability to do these [measurements] at a long distance. That’s the challenge of working with thermal cameras if you have a limited budget. [The toucan] would be a minor blob [if we took the videos from a long distance],” Tattersall said.
Images were collected every 10 seconds for approximately 6 hours per day per toucan, corresponding to a total of 30,000 frames of video over 110 hours, or 12 to 24 hours per toucan, as reported in the July 24, 2009, issue of Science. Tattersall’s Web site, www.brocku.ca/researchers/glenn_tattersall/.com, offers videos and images from the study.
The videos and images confirmed the hypothesis that the toucan uses its bill to keep cool. “I would say that we have data that shows that [toucans can regulate their blood flow],” Tattersall said. “It’s backed up with other birds. It’s backed up from a logical perspective.” He believes that temperature regulation did not drive the bill to be large, but rather that the bill’s cooling function constrains the toucan to its tropical habitat.
The bill has been shown to have other functions as well. The bill is used to eat fruit, and the coloration of the bill is used for communication and aggression. However, the sexual ornament hypothesis is unlikely because the bill is similar in coloration, size and shape for males and females. On the other hand, the males have a slightly larger bill, and the birds possibly can detect this size difference.