Lawrie Conole wrote:
> >
> > Can't answer this one; but I guess they'd be snap-frozen if they were more
> > than a few thousand metres up.
Alerstam book "Bird Migration" refers to an experiment in Sweden where
researchers where able to measure altitude of Common Swifts on their
return flight of several hundred kms to their nest. In clear weather
the average altitude was 2300m 10 of 50 swifts had flown
to altitudes over 3000m. The highest was 3600m.
In the discussion of migration flight altitude Alerstam mentions as
an extreme a plane collision with a Ruppell's Vulture at 11,000m.
The reduction in partial pressure of oxygen at higher altitudes is less of
a problem for birds because of the efficiency of their respiratory system.
To some extent the cooler temperatures at higher altitudes can be helpful
to migrating birds because water loss is reduced. This may be relevant
to Swifts.
Andrew Taylor
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