Mark Chappell wrote:
>
> A few items concerning bird lungs....
>
> I've done some research on bird and mammal ventilation (breathing),
> although that's not my main area of interest. I suspect that during
> flight, there will be synchrony between wingbeat and ventilation
> cycles --
> although not necessarily in a 1:1 ratio. In other words, inhalation
> might
> occur every second, third, or fourth wing stroke (the same thing
> occurs in
> running mammals -- ask any distance runner you know). However, when
> not
> flying the movement of air is generated in the 'usual' way, via
> muscular
> activity not related to wing motion. Birds actually breath fairly
> slowly
> for their mass (relative to mammals) and I very much doubt if
> breathing
> cycles are anywhere near as fast as wingbeat frequency. I once worked
> on
> hummingbirds, which have wingbeat frequencies of perhaps 50
> cycles/second
> or higher. My resting hummers never breathed faster than maybe 6-8
> breaths/second, even at very high metabolic rates (in other words,
> high
> demand for oxygen). I have also studied Adelie penguins; at rest they
> breath maybe 6-10 times/minute but when 'flying' underwater they cycle
> their flippers several times/second.
>
> Another point alluded to in earlier messages concerned the 'superior'
> quality of the avian lung compared to the mammalian lung. It's true
> that
> at extreme altitudes the unidirectional flow in a bird lung seems to
> work
> better than the tidal system in a mammal lung (bar-headed geese
> routinely
> migrate over the top of Mt. Everest, an altitude that will quickly
> kill
> most un-acclimated humans). But there's little evidence that in more
> reasonable conditions the bird system is 'superior', in terms of
> supplying
> the oxygen needed for metabolic power production. As an obvious
> example,
> there are flying mammals (bats) which can produce the same power
> output as
> equivalently-sized birds -- and they do this with a typical mammalian
> lung.
> Also, if you look at the maximum power output of birds vs. mammals
> relative
> to the resting metabolic rate, it turns out that the highest
> performers
> are... mammals! The highest power output from birds is maybe 15-20
> times
> greater than resting metabolism. However, in certain athletic mammals
> (racehorses, antelope, kangaroos), maximum power output is 40 times
> greater
> than resting metabolism. Good human athletes can accomplish a 15-20 X
> increase above resting metabolism.
>
> Finally, it was suggested in an earlier message that the
> unidirectional
> bird lung removed "most" of the oxygen in respired air. This is a
> little
> bit of an exaggeration. We physiologists use the term "oxygen
> extraction"
> for the ratio of [oxygen in expired air/oxygen in inspired air]. A
> typical oxygen extraction for a resting bird is about the same as for
> a
> typical resting mammal -- 20-30% or so (this means that inspired air
> contains 21% oxygen and expired air contains 15-17% oxygen). The
> maximum
> oxygen extraction measured for birds is about 60-70% -- very high, but
> this
> occurs only in a few species and only under special conditions (like
> when
> it's very cold). And some mammals can extract almost as much oxygen.
>
> So although from our human engineering perspective the bird lung seems
> to
> be a better 'design' than the mammalian lung, under most circumstances
> the
> ability of birds to supply oxygen for metabolic power production
> doesn't
> appear to be 'superior' to mammals.
>
> Hope this is of interest and doesn't contain too much nerdy scientific
> jargon.... Mark Chappell
>
> >OK, we have had descriptions of birds' respiratory system, including
> one
> >sent to me personally by a US correspondent, who very kindly also
> scanned a
> >page from one of those 'basic biology texts' that Philip V* quite
> rightly
> >said we should all have consulted first (:-)).
> >
> >However there is still a question unanswered: someone has written
> saying
> >more or less that birds breathe many times faster than their wings
> beat, so
> >any vocalisation
> >should be independent, but someone else has stated that the
> wing-beats are
> >the mechanism that drives air through the system. Which is correct?
> >
> >John Leonard
>
> ****************************************
> Mark Chappell, Biology Department, UC Riverside
> until Aug '99: C/O Dr. Bill Buttemer
> Dept. Biological Sciences, University of Wollongong
> Wollongong NSW 2522 AUSTRALIA
> email:
> web: http://cnas.ucr.edu/~bio/faculty/Chappell.html
> ****************************************
>
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o
Thankyou Mark for the information. Answered some things I've always
wanted to know.
I've seen a Little Penguin 'flying' underwater and coming to surface to
breathe while continiung to whizz along under surface - reminiscent of a
Swallow drinking.
I'm sure it must have made at least 10 strokes per breath as it rounded
up a school of anchovies and very efficiently creamed off the outermost
individuals from the school.
Incidentally a horse galloping can only take one breath per stride, or
so I am told. The mass of the innards tends to slosh against the
diaphragm which powers the exhalation phase. The horse can't take an
extra breath anywhere. This is probably why despite intense selection,
racehorses seem to reached peak speed possible.
I have no idea if the same applies to other ungulates, or to other
mammals eg dogs. And what about kangaroos?
Birds of course have a rigid frame fuselage and no diaphragm.
I continue to wonder how the diaphragm arose in mammals, and how the
air-sac arrangement can have originated in birds, from their respective
reptilian ancestors.
Anthea Fleming in Melbourne.
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