Philip Veerman wrote:
>Birds, because of their metabolism, find it difficult to
>hibernate.
I'm not sure this is true. Torpor is known from several groups of birds.
Hummingbirds are common textbook examples. Migrating Rufous Hummingbirds
have been observed to apparently choose exposed roost sites to maximise
the depth and length of their overnight torpor.
Metabolic rates are proportional to temperature, so by pushing their
temperature down as quickly and as long as possible, they are minimizing
their energy consumption through the night. One Rufous Hummingbird
was calculated to have saved 10% of its fat reserve by entering such an
overnight torpor.
Extended torpor, such as the winter hibernation of weeks or months seen
in nearctic/palearctic mammals, does seem to rare in birds. I believe
its only been recorded for Common Poorwills.
This doesn't mean extended torpor is unavailable to birds. It may just
indicate that other better strategies are available to them.
Movement/migration is easier for birds than many animals. The Mountain
Pygmy Possums which hibernate in the Australian Alps, don't have the
option of moving to areas 100s km away during the colder months.
Short periods of torpor, such as the hummingbird's overnight torpor,
may not be available to larger animals because their thermal inertia
prevents their temperature falling quickly enough.
Little seems known about torpor in Australia birds. Its been induced
in captive Spotted Nightjars. There is recent research with observations
of Tawny Frogmouths entering two phases of torpor during winter nights
and Autralian Owlet-nightjars entering torpor during winter days.
Both these observations are near Armidale (northern NSW) and it will be
interesting to find out what these birds do elsewhere in their range.
For those interested the refs of this recent research are;
G. Kortner, R. M. Brigham, and F. Geiser (2000) WInter Torpor in A
Large Bird. Nature 407 p318, 21 Sept. 2000.
G. Kortner, R. M. Brigham, and F. Geiser (2001) Torpor in Tawny
Frogmouths. Physiol Biochem Zool 74:789-79
R. M. Brigham, G. Kortner, T. A. Maddocks, and F. Geiser (2000) Use of
Torpor by Owlet-Nightjars. Physiol Biochem Zool 73:613-620
One of the authors seems to have the papers available as:
http://www.uregina.ca/biology/faculty/brigham/PDF%20files/Brigham%20et%20al.%202000.pdf
http://www.uregina.ca/biology/faculty/brigham/PDF%20files/Frogmouths%20Nature.pdf
http://www.uregina.ca/biology/faculty/brigham/PDF%20files/Kortner%20et%20al.%202001.pdf
Andrew Taylor
Birding-Aus is on the Web at
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