Forster's tern Sterna forsteri

Identification Tips:

Adult alternate:

Adult basic:



Similar species:

When identifying terns, it is safest to rely on a combination of field marks. In most plumages the Forster's Tern has two field marks that separate it from the similar Common, Arctic, and Roseate terns: a black eye patch and white primaries that contrast with the gray upperparts. In alternate plumage, Common and Arctic terns have gray not white underparts while the Roseate Tern often has a darker bill. Common and Arctic terns have dark outer edges of the tail and white inner edges; just the opposite of the Forster's. The undersurface of the primaries is a useful feature for separating the Forster's Tern from Arctic and Roseate terns. The Forster's Tern has a broad, blurry trailing edge to the primaries where it is thin and crisp in the Arctic and very restricted in the Roseate. On the upper surface of the primaries, the Common Tern has a dark wedge that is lacking in the Forster's Tern. The larger Sterna terns (Royal, Elegant, Caspian) have entirely orange or red bills, much larger bodies, broader wings, shorter tails and ragged crests at rear of head.

Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.