Gull
chicks are semiprecocial: they hatch with their eyes open,
covered with down, and able to walk; but unlike fully
precocial chicks, they remain in or near the nest for the
first two or three weeks. For the next several weeks they
hide in nearby vegetation (when available) until they
fledge. Both adults feed the chicks regurgitated meals at
least through fledging and, in some species (such as the
Herring Gull), for a considerable post-fledging period. To
elicit the adult's feeding response, the chicks peck at the
adult's bill, which is often adorned with a "target" -- a
contrasting spot. When juvenile gulls are
fledged they do not look like their parents, but instead
have a distinctive streaked brown plumage. As the birds
mature, the patterns of the plumage change, and these
changes differ among gull species. Some gulls, such as
Franklin's and Bonaparte's, develop adult plumage and breed
when they are two years old. Others do not reproduce until
they are three (i.e., Ring-billed, Heermann's Yellow-footed)
or four years old (i.e., California, Western, Thayer's,
Herring, and Lesser and Great Black-backed Gulls). The
largest gulls, such as the Herring and the Black-backs, may
even take five years to reach maturity. Adults usually have
different breeding and winter plumages; thus, to identify
gulls one must often differentiate among five or more color
patterns within a species. Occasionally immature gulls
may form pairs, construct nests, and copulate, but not lay
eggs. Such "practice" may increase the gulls' chances of
success once their testes and ovaries mature and they are
actually able to reproduce. SEE: Precocial
and Altricial Young;
The
Color of Birds;
Eye
Color and Development. Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.