Gull Development

photographs of a Ring-billed Gull (top) and a California Gull (bottom) by Rohan Kamath
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.