At 08:30 PM 4/5/98 +0900, Des Allen wrote:
>I can't but I enjoy speculating...
>
>I would want all of the above features but I would certainly not shunt
>blood away from the muscles. when I am a penguin I can expect my dive to be
>over in a relatively short time and then I can recover. When I am migrating
>across the Himalayas this is not the case . I would want a high metabolic
>rate to keep me warm, very efficient, highly aerobic fat metabolism to make
>best use of the weight I have to carry. thick feathering would keep me
>warmer up there than down in the bottom of the sea, but I might want to
>have thick eyelids to stop my eyes freezing up.
>I would also favour a countercurrent system in my neck (or whatever birds
>have) like desert mammals to reabsorb exhaled moisture, especially since I
>have thinner lung tissue which presumably increases exhaled moisture. Many
>longnecked birds migrate at high altitudes - is there a connection?
>
Hi Des,
Yes, it is fun speculating about these things.
My feeling is that increased activity through beating of the wings,
increased heart beat, and other muscular activity would increase the
metabolic rates of high flying birds. Increased metabolism would thus
increase the production of body heat.
All the highest flying birds are among the largest fliers. I suspect that
this has something to do with conservation of body heat and water. The body
surface area to body volume ratio is increased in smaller animals and, as a
consequence, body heat and body water is lost more readily to the
surrounding environment (unless there is suitable body insulation which
slows down this loss).
I recall reading a paper in a physiology journal in the mid 1980s suggesting
that small birds (e.g long-distance migratory waders) may in fact go into
torpor during long-distance flights to survive low temperatures and to
conserve energy. They would thus glide on air currents during the times they
are torpid. This may explain why some waders are found way outside their
normal migratory range ... they could have been blown way off course while
they are in a torpid state. An interesting speculation, anyway ...
I can't remember the title or the authors of this paper, does anybody else
know?
Your comments about long necks is also interesting. As far as I'm aware,
most recycling of exhaled moisture through countercurrent mechanisms occurs
in the nasal passages of birds, as in mammals, rather than in the neck
region. However, some birds engage in evaporative cooling by gular
fluttering (rapid vibration of the throat region to evaporate water on its
moist surface). Perhaps a long neck allows a greater surface area for
evaporative cooling during times of great physical activity.
Best wishes,
Stephen
**************************************************************
Dr Stephen Ambrose
Research Manager
Birds Australia (Royal Australasian Ornithologists Union)
Australian Bird Research Centre
415 Riversdale Road,
Hawthorn East,
VIC 3123.
Tel: +61 3 9882 2622
Fax: +61 3 9882 2677
Email: S.Ambrose <> (at work)
<> (at home)
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