[bcbirdclub] Re: Fw: Using your beak to cool off
- From: "Jerry Thornhill" <mjt@xxxxxxxxxxx>
- To: "'BCBC Listserve'" <bcbirdclub@xxxxxxxxxxxxx>
- Date: Tue, 28 Jul 2009 19:31:30 -0400
Flush an uninsulated body part with blood to cool off, huh. Well, if Roger
& I can just figure out how to flush our scalps with blood, we'll be the
coolest guys around. Come to think of it, we are the coolest guys around.
Jerry
-----Original Message-----
From: bcbirdclub-bounce@xxxxxxxxxxxxx
[mailto:bcbirdclub-bounce@xxxxxxxxxxxxx] On Behalf Of Roger Mayhorn
Sent: Tuesday, July 28, 2009 5:44 PM
To: BCBC Listserve
Subject: [bcbirdclub] Fw: Using your beak to cool off
Hi Everyone,
This post appeared on another listserve and I thought it interesting enough
to pass it on.
Roger Mayhorn
>
> 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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