Larus marinus
Order Charadriiformes
Family Laridae
Subfamily Larinae
Adult in summer.— Tail and under parts pure white; back and wings apparently black (really dark brown); wings edged posteriorly with white; bill yellow; feet pale flesh-color.
Adult in winter.— Similar, but top of head and hind neck streaked with dusky.
Immature.— Upper parts dusky, tail dusky, crossed near the tip by a narrow band of brownish-white; head, neck, and under parts white, streaked and washed with brown.
Nest, of grass, moss, etc., either on the ground or in trees.
Eggs, grayish-brown, blotched with chocolate.
The Black-backed Gull is a winter resident along the seacoast of New York and New England. A few individuals arrive in August, and a few linger till May, but the species is commonest in the winter months. It is much less common, however, than the Herring Gull, and as a rule keeps to the outer shores and beaches. Occasionally, however, one or two may be observed in a harbor or even in a fresh-water pond near the sea; there are generally one or two among the Herring Gulls that gather off T wharf in Boston. A common cry of the Black-backed Gull is a harsh kyow, suggesting the note of the Green Heron.
When a large flock of gulls are standing on a flat or sandbar, the mature Black-backed Gulls will be easily distinguished from the Herring Gulls, if they stand with their backs and sides toward the observer; the black wings and back will then present a striking contrast to the pure white head and neck. To identify a bird when flying, one must be sure to get a view of the upper part of the wings; even a Herring Gull will often appear to have dark wings, when the under surface is seen in shadow. The immature Black-backed Gulls can often be told from the immature Herring Gulls only if the two stand side by side, when the difference in size becomes apparent.
Hoffmann – A Guide to the Birds of New England and Eastern New York (1904)