Dear Peter and Andrew,
The physiological adaptations of penguins to diving relate to the
circulatory rather than to the structure of the respiratory system. So the
functions of the air-sacs appear to remain the same as in other bird species.
Kooyman (1975) says:
" How a diving penguin, particularly the Emperor Penguin, avoids nitrogen
narcosis or decompression sickness is unknown.
"The bulk of the gas contained in the respiratory system of penguins is in
the air sacs, the non respiratory portion of the system. The opposite is
true in mammals. A priori it might be expected that in order to avoid
absorption of nitrogen during deep dives a valving system might evolve that
would isolate air sacs from the lungs. No such feature has been described in
any diving bird. Furthermore, such a response would isolate the major oxygen
store of the bird. Published observations on arterial gas tensions during
deep dives show that gas exchange in Adelie and Gentoo Penguins continues
between the lungs and air sacs. The conclusion is that most dives are too
short for significant amounts of nitrogen to be absorbed.
"Unlike seals which exhale to about 50-60% of inspiratory lung volume before
diving (Kooyman et al. 1971), penguins appear to dive after an inspiration
(Kooyman et al. 1973, 1982). The result is that the diving gas volume
relative to body weight of penguins of about 160 cubic cm/kg is much greater
than seals which is 22 cubic cm/kg. In contrast to seals the contribution of
the lung-air sac system to total body oxygen stores in the penguin is
significant."
I haven't found anything more recent than this that sheds further light on
the respiratory physiology of diving penguins. Perhaps others know of
additional material.
References:
Kooyman, G.L. (1975). Behaviour and physiology of diving. In: The Biology of
Penguins (ed. B. Stonehouse) pp. 115-37.
Kooyman, G.L., Davis, R.W., Croxall, J.P. & Costa, D.P. (1982). Diving
depths and energy requirements of King Penguins. Science. 217: 726-7.
Kooyman, G.L., Drabek, C.M., Elsner, R. & Campbell, W.B. (1971). Diving of
the Emperor Penguin, Aptenodytes forsteri. Auk. 88: 775-95.
Kooyman, G.L., Schroeder, J.P., Greene, D.G., & Smith, V.A. (1973). Blood
nitrogen tensions of seals during simulated deep dives. Amer. J. Physiol.
223: 1016-20.
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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