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How to Cool Off Using the AssA mechanism found in birds and maybe mammals, too |
By Stefan Anitei, Science Editor
16th of February 2007, 11:22 GMT
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Elephants flap their huge ears to dissipate heat, dogs pant to cool off, and people cool down by sweating all over.
Crocodiles are seen staying still with their mouths opened wide for the same purpose.
In fact, mammals have more or less developed the sweating glands that help them balance the body temperature. And panting is common in birds and mammals, as it employs water evaporation that carries out of the body heat. Pelicans and related birds are known to flap their bill pouches for eliminating excessive heat. But this behavior is isolated.
Anyway, for birds, keeping a constant temperature is more difficult than for mammals, as they lack the sweat glands, even
if water still leaks out of their skin and evaporates.
Recently, a research team got an explanation: birds employ their "tushy" to get rid off the excessive amount of heat and it seems that mammals, too, could use this mechanism via their anuses (except platypus and echidna, mammals do not have cloaca). A team led by physiologist Ty Hoffman at Arizona State University, investigated this possibility regarding the cloaca (photo above, of a parrot), the opening that is the common termination of the intestinal, urinary and genital tracts of amphibians, reptiles, birds and monotreme mammals (platypus and echidna).
In 2004, animal physiologist Dale DeNardo together with Hoffman's team discovered that Gila monsters (venomous lizards from southwestern US and northwestern Mexico) are able to decrease their body temperature by as much as about 5 degrees F (3 degrees C) via their cloacae.
This time, Hoffman's team studied Inca doves (photo below), birds inhabiting deserts and semideserts in North and Central America, where they are exposed to a great deal of thermal stress. Each individual was put in a glass chamber divided into two sections, one above other, by a latex sheet with a hole through which only the bird's head could pass.
The top chamber caught water that was shed through the bird's mouth, while the bottom section registered water loss through the bird's skin and cloaca. The researchers sealed the birds' cloacae with glue. (which was removed after the investigations) in order to assess only the skin's water loss.
Comparison birds lost much more water at very high temperatures compared to the birds with tapped cloacae, thus the doves were dissipating water through their cloacae to cool off.
At roughly 42° C, water loss though the cloaca represented almost a quarter of the total water loss, almost as much as that lost via panting. More investigations would assess how common is this mechanism among birds. "Perhaps mammals employ anal evaporation," Hoffman said.
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