Even
when apparently asleep, birds open their eyes and peek
around. Peeking is limited to the phase of sleep referred to
as dozing or "quiet sleep." During the remaining
"active-sleep" portion of their slumber, birds' eyes remain
shut. Animal behaviorist Dennis Lendrem surveyed flocks of
dozing ducks until the patterns of peeking could be
discerned. Lendrem found that in the
ducks peeking typically occurred about once every two to six
seconds. Which birds in the flock do the most peeking
depends on the number of coflockers, positions in the flock,
and the time of year. Members of smaller flocks peek more,
as do birds in less-protected positions and those closer to
a perceived threat. During the breeding season, males peek
more than females. This seems to be due, in part, to sexual
activities of the flock. As the number of females in the
flock increases, so do the opportunities for the males to
engage in promiscuous sex, which means that males must keep
an eye on each other. Similarly, there is always the threat
of paired females (willingly and unwillingly) copulating
with males other than their mates. That would explain why
mated males peek more than bachelor males. But being attractive to
females carries some potential costs. Brightly plumed
breeding males presumably are quite conspicuous to
predators. Breeding males peek much more frequently than
they do after they return to their eclipse plumage when, all
other factors being equal, their peeking rates drop to those
of females. How much active sleep birds
require is still unknown. Different sleep phases produce
different heart and respiratory rates and changes in
electroencephalograph (EEG) patterns, as they do in people.
It has been suggested that birds that move around often and
rapidly require a greater proportion of active sleep than
more intermittently active birds, which exhibit more
irregular sleep patterns. Dozing and peeking in flocks allow
for more active sleep, reduce the threat of predation, and
for some males, increase mating opportunities. SEE: Communal
Roosting;
Flock
Defense. Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.