Chlidonias niger
Order Charadriiformes
Family Laridae
Subfamily Sterninae
Adult in early summer.— Head, neck, and under parts sooty-black; feathers under the tail white; back, wings, and tail dark gray; bill black.
Adult in late summer and autumn.— Head, neck, and under parts white; top of head and stripe back of eye dusky; back, wings, and tail deep pearl-gray; bill black.
Immature.— Similar to fall adult, but upper parts browner; sides washed with dusky.
The Black Tern is a rather irregular migrant along the coast of New York and New England in summer and early autumn. It is rarely seen in its adult black plumage, though it is occasionally seen with under parts spotted with black and white. Even in the autumn plumage it may be readily distinguished from any other tern, except the Least, by its small size. Its tail, too, is less deeply forked than in other adult terns. From the adult Least Tern it may be distinguished by the dark gray of its upper parts and by its black bill. An immature Least Tern has a blackish bill, but is considerably smaller than a Black Tern, and has a brownish tinge on its upper parts.
Hoffmann – A Guide to the Birds of New England and Eastern New York (1904)