American Herring Gull

The American Herring Gull is the common large 'gray-backed' gull of North America, closely related to and formerly considered the same species as the Eurasian Herring Gull. It shows the same classic gull plumage pattern of pale gray back, white head and underparts, and black-tipped wings, and like its Old World counterpart takes several years to mature through a series of mottled brown immature plumages.

Adult mantle feathers are pale to medium gray, similar in shade to Eurasian Herring Gull though averaging slightly darker in some populations, contrasting with clean white head and underparts feathers. Outer primary feathers are black with white tips and one or two white mirrors near the tip. Immature birds in their first year show heavily mottled brown and buff feathers throughout, gradually acquiring gray back feathers and reducing brown mottling over about four years. Winter adults show brownish streaking on the head, unlike the pure white head of breeding adults. Distinguishing this species from Eurasian Herring Gull by feather alone is difficult and often relies on subtle differences in gray tone, wingtip pattern extent, and overall structure rather than a single diagnostic feather feature.

Sexes look alike, with males averaging larger. This is a four-year gull, progressing through a series of increasingly gray, less mottled brown plumages annually before reaching full adult pattern around the fourth year. Nonbreeding adults show streaked brownish head and neck feathers, molting to a clean white head for the breeding season. A complete post-breeding molt replaces flight feathers over an extended period, typically completed before winter.

Breeds along coastlines, offshore islands, and around the Great Lakes and other large inland waters across Canada and the northern United States. Outside the breeding season it ranges more broadly along coasts, large rivers, lakes, and landfills throughout much of North America, with northern populations migrating south in winter while others remain closer to breeding areas year-round.

American Herring Gulls are opportunistic feeders, taking fish, invertebrates, carrion, and refuse, and are frequent visitors to landfills, harbors, and fishing operations, as well as natural coastal and lake habitats. Nests are built on the ground, cliff ledges, or occasionally rooftops, often in colonies, with both parents sharing incubation and chick-rearing. Its call is a loud, wailing series similar to other large gulls. Conservation status is IUCN Least Concern.