Migration

Dispersal begins late Jul, but few individuals leave breeding areas (Moore 1976). Only nonbreeding birds appear migratory; most adults remain near breeding grounds throughout year (Drury and Nisbet 1972, Moore 1976). First-year birds winter in southern portions of range, with second- and third-year birds moving intermediate distances. Adults disperse away from breeding colonies in Aug, return to colonies in Apr (Moore 1976). In late fall and winter, apparent major offshore movement of Herring Gulls in ne. U.S., Canadian Maritimes (Powers 1983). Other individuals disperse south to areas of open water in fall. Subadults concentrate along southern Atlantic Coast and Gulf Coast during winter (Moore 1976). Some overwinter in large freshwater reservoirs in Midwest. A few move south along Pacific Coast and overwinter south to California (RJP).

European populations considered nonmigratory, although there is dispersal outside breeding season. Only Baltic populations experience severe winter conditions encountered by North American Herring Gulls in Great Lakes and n. Canada.

Dispersal away from breeding colonies probably on individual basis. Some young remain with parent(s) for several months postfledging (Burger 1984, RJP). Juvenile and immature birds congregate around areas where food reliably obtained, e.g., intertidal areas, fishing boats, refuse dumps. Adults (and many immatures) found offshore Oct through Mar (Powers 1983, RJP). Great Lakes adults remain near breeding colonies; most immatures disperse southward Oct to Feb (Moore 1976).

Offshore movement related to foraging conditions. Many adults offshore in Mar building reserves for breeding season. These move onshore in Apr to breed (RJP). Immatures move to milder (less energetically stressful) southern climates when cold weather starts (Oct–Mar).