Page 57 - Das Wunder der Migration bei Tieren

At al ti tu des such as 6,000 me ters (19,690 feet) whe re the
oxy gen con tent is half that of gro und
le vel, birds can still fly with ea se, whe re a per son who is
stan ding still may ha ve dif fi culty bre at hing. At al ti tu des
abo ve 7,000 me ters (23,000 feet), a
per son wit ho ut physi cal tra ining may lap se in to un cons -
ci ous ness and die. Ho we ver, a flock of
migrating whooper swans has be en ob ser ved
flying at 8,230 meters (26.904 feet) above sea level.

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