[TN-Bird] Using your beak to cool off

From: "Charles P. Nicholson" <cpnichol@xxxxxxxxxxxxx>
To: tn-bird@xxxxxxxxxxxxx
Date: Mon, 27 Jul 2009 17:16:56 -0700 (PDT)
It has been known for some time that birds' beaks have a roll in controlling 
the bird's body temperature (thermoregulate).  The following article from 
http://sciencenow.sciencemag.org/cgi/content/full/2009/723/2?etoc helps explain 
how this works in a toucan.
Chuck Nicholson
Norris, TN
A Bird With a Big Air-Conditioning Bill



By Michael Price
ScienceNOW Daily News
23 July 2009
When it comes to keeping cool, toucans get top billing in the animal
world. New research shows that the colorful bird uses its massive beak
to rapidly radiate away heat, allowing it to chill out in tropical
climates or when expending a lot of energy while flying. At its most
efficient, the toucan is theoretically capable of jettisoning 100% of
its overall body heat loss through its bill.
Birds don't sweat. Neither do elephants or rabbits. Instead, these
creatures flush an uninsulated body part--such as a beak or an
ear--with blood and let the heat dissipate into the air. Glenn
Tattersall, an evolutionary physiologist at Brock University in Canada,
wanted to find out just how much of a cooling effect the toucan's giant
beak provided. 

He and colleagues focused on the South American toco toucan (Ramphastos toco),
which has the largest bill of any bird relative to its body size. (It
can represent between 30% and 50% of the creature's overall body
surface area.) The team then used infrared thermal scanners to record
the bill's surface temperature while the bird was exposed to air
ranging from 10° to 35°C--temperatures typical of the toucan's
habitat--and also while flying. By comparing the temperature of the
bill with the environmental temperature, Tattersall's team was able to
gauge how much heat was being lost; the larger the difference, the more
heat was escaping.  The bill radiated a great deal of heat at
high temperatures and when the toucan flew, indicating that, like
elephants and rabbits do with their ears, the toucans flush their bills
with blood to cool down. At lower temperatures, the difference between
air temperature and bill temperature dropped, meaning that the toucans
were restricting blood flow to their bills. Based on its size, a
toucan's bill can theoretically account for anywhere from 5% to 100% of
the bird's body heat loss, the team reports tomorrow in Science.
When the toucan is in flight, its bill is the most efficient
heat-shedder ever reported, losing four times more heat than the bird
produces while at rest. That's about four times more efficient than
either elephants' ears or ducks' bills.  Juvenile toucans in
the experiment didn't have as much control over how much blood flows
into their bills. Why is unclear, but Tattersall says that "our best
guess is that the control over the vessels takes time to develop, or
the blood vessels in juveniles are much denser than in adults and are
less capable of being controlled." 
Gary Ritchison, an ornithologist at Eastern Kentucky University in
Richmond, says that the study shows that toucans do use their bills to
regulate body temperature. But that may not be the reason why toucans'
bills evolved to be so large. "You'd have to expect that it's not the
overriding explanation [for bill size]," he says. There are too many
other considerations, such as defense and diet, to know for sure, he
says. 
Tattersall agrees but adds that biologists need to consider
thermoregulation when discussing bird beak evolution. Most papers have
tried to link bill size to the birds' diets. Even in birds with small
bills, he says, there's evidence that "the bill is still a site of heat
exchange and therefore under some selective forces in terms of
thermoregulatory constraints.




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[TN-Bird] Using your beak to cool off

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