*** I can't resist more pontification on this (I do a lot of science stuff
in this area...) -- Mark
>On the oxygen thing and following up recent lung-derived e-mails,
>
>I have always been of the understanding that the highest SUSTAINED
>energy turnover in humans is achieved by Tour de France cyclists and
>Swedish woodcutters, but that these were only in the 4 times basal
>metabolic rate region (correct me if I am wrong, as I don't have
>refernces to back me up). There is a lot of literature from both
>mammals and birds looking for the existence of and an explanation
>for a proposed metabolic ceiling of about 5-7 X BMR, but it seems to
>me that in the medium term (ie. not instantaneous & 'sprint' levels,
>and not over the long-term, such as whole breeding seasons) birds
>must surely take the cake.
**** The "sustained" measure is over a period of days or weeks and is
equivalent to the "daily energy expenditure" (DEE) numbers I mentioned.
And you are right; I think the highest DEE in humans is in cyclists and is
about 4-5 X BMR. Among birds and mammals, I think the highest known DEE is
in a little Aussie marsupial called a dunnart (Sminthopsis), which came out
to be about 8 or 9 X BMR (this is cheating a bit because marsupial resting
metabolism is lower than that of birds or placentals). And you're
absolutely right, there is a lot of debate over the 5-7 X BMR figure. That
range includes most of the species measured during breeding (when
presumably energy consumption is high because parents are caring for young
in addition to themselves). But this isn't necessarily any kind of
physiological limit (in other words, there's no convincing data that birds
couldn't expend more energy if they 'wanted' to). There are other factors
besides physiology that limit energy expenditures during breeding (like
risks of predation and so forth).
>
>A shorebird flying for 5,500 km is presumably expending energy at
>anything from 10-15 X BMR (depending on your estimate of the energy
>costs of flight) continuously for about 4 days. That is at a rate 3-4
>times higher than what humans can sustain, for over a hundred hours
>without a break!
*** I would guess more like 6-8 X BMR (remember, they're flying at the most
'efficient' speed, not at full power) for perhaps 2 days or a bit more
(shorebirds fly pretty fast, and many studies have indicated that birds
take full advantage of storm fronts or winds when they can). And this
isn't really comparable to the "sustainable" DEE measures, since at the end
of such a flight the bird is exhausted and pretty much out of fuel, and
cannot do a repeat performance without a long period of recovery. But
despite such disclaimers, it's still pretty damn impressive.
****************************************
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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