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Birds need far less sleep
than humans do. Birds probably sleep to
relax their muscles and conserve energy
but not to refresh their brains. Many seabirds,
in particular, sleep very little. For example,
the sooty tern, which rarely lands on water,
may fly for several years with only brief
periods of sleep lasting a few seconds each.
Flying is so effortless for the sooty tern
and some other seabirds that it takes virtually
no energy at all.
Most birds are active during
the day and sleep at night. Exceptions are
birds that hunt at night, such as owls and
nightjars. Birds use nests for sleeping
only during the breeding season. The rest
of the year, birds sleep in shrubs, on tree
branches, in holes in trees, and on the
bare ground. Most ducks sleep on the water.
Many birds stand while they sleep, and some
birds sleep while perched on a branch-sometimes
using only one foot. These birds are able
to avoid falling over because of a muscle
arrangement that causes their claws to tighten
when they bend their legs to relax.
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