Re: High altitude fliers

Subject: Re: High altitude fliers
Date: Sun, 5 Apr 1998 20:30:32 +0900
At  5:18 PM 98.4.4 +1000, Stephen Ambrose wrote:
>My faithful Prosser (1974) states that high fliers have:
>1.  Higher haemoglobin levels (molecules that bind with oxygen to carry it
>from the lungs to other body tissues);
>2.  A greater concentration of red blood cells in the blood (they carry the
>haemoglobin molecules);
>3.  Higher myoglobin levels in the muscles. Myoglobin binds to the oxygen
>molecules that are delivered to muscle tissue.
>4.  A more powerful heart to pump oxygenated blood around the body.
>1.  Greater air sac and lung volume, thus allowing larger tidal volumes;
>2.  A greater network of blood capillaries taking up oxygen from the lungs;
>3.  Thinner lung tissue, thus reducing the distance that oxygen molecules
>need to diffuse into the blood capillaries.
>Do high fliers also shunt blood to essential organs such as the brain and
>heart, have depressed metabolic rates, and greater toleration to build up
>in lactic acid, as in diving birds? 
>How do they thermoregulate effectively at altitudes where ambient
>temperatures are extremely low?  There would also be a risk of excessive
>loss of body water at such high altitudes and flight activity, so how do
>these birds avoid excessive dehydration?
>Can anyone else answer these questions?

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?

Des Allen


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