New York Natural Heritage Program
Forster's Tern
Sterna forsteri Nuttall, 1834
Birds

General Description [-]
The Forster's Tern is a medium-sized tern most often occurring in and around marshes. They are white below, pale grey above, with a black cap and mostly orange bill.

Identifying Characteristics [-]
Forster's Terns are a medium-sized tern most often occurring in and around marshes. They measure 33-36 cm (13.0-14.2 in.) in length and weigh 130-190 g (4.6-6.7 oz.). The sexes appear similar (Mcnicholl et al. 2001). The adult breeding plumage is white below, pale grey above, with a black cap and nape. The birds have a mostly orange bill, orange legs, and orange feet. They have a long, deeply forked grey tail with white outer edges. When they are in flight, the upperwing area appears pale due to the grey primaries (long flight feathers that extend along the outer edge of the wings), and the white rump contrasts with the grey back and tail (National Geographic Society 1983). The adult nonbreeding plumage has a black "mask" around the eye and over the ears instead of a black cap. The mask does not reach the nape or rear of the top of the head. The forehead is white, bill is black, and feet are orange (Mcnicholl et al. 2001). Compared to adults, juveniles and first-winter birds have shorter tails and generally more dark color in the wings and darker primaries. Juveniles have a brown cap, dark eye patch, and a faint or absent bar on the shoulder. Calls of Forster's Terns include a hoarse "kyarr" that is lower and shorter than that of Common Terns (Sterna hirundo). They nest in colonies that are widely spaced in marshes (National Geographic Society 1983). Nests can occur as scrapes in the mud or sand with little or no lining, in clumps of vegetation or on floating vegetative mats, or on top of muskrat lodges (Mcnicholl et al. 2001). Clutches usually contain two to three eggs. Less often, they contain one or four, and very rarely, up to six. The background color of the eggs is usually olive to buff or pinkish buff, with many brown spots, small blotches, and crooked lines that often decorate the larger end (Bent 1921, Mcnicholl 1971). The eggs are smooth, but not glossy (Harrison 1979).

Characters Most Useful for Identification [-]
The combination of characterstics that distinguish this species are: a tern with a pale grey back, black cap, orange legs and bill (with a black tip), long legs and bill, and deeply forked tail (National Geographic Society 1999).

Best Life Stage for Proper Identification [-]
Adults in breeding plumage are easiest to identify but juveniles and birds in their winter plumage can also be distinguished from other tern species.

Behavior [-]
Forster's Terns forage aerially over flooded mudflats or calm waters for insects and fish. They may forage alone or in mixed-species foraging aggregations (Schreffler et al. 2010). Pairs are monogamous, at least for the breeding season. They may nest colonially, co-occuring with other Larids including Common Terns (Sterna hirundo) and Laughing Gulls (Larus atricilla). Forster's Terns are territorial during the courtship period. A study of California Forster's Terns found that colonies were attended in roughly equal amounts by males and females, with the females more frequently present at night and the males more frequently present during the day (Bluso-Demers et al. 2010).

Diet [-]
The diet of the Forster's Tern consists mainly of small fish and arthropods (McNicholl et al. 2001).
Forster's Tern Images
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The Best Time to See
Forster's Terns may be observed in NY in the spring, summer, or fall. Breeding individuals are present on Long Island from late May into August. Forster's Terns may appear along the coast or Great Lakes during spring (April into May) or fall migration (mid to late August through November), and are more common in the fall (Levine 1998). They are also found along the lower Hudson River (mostly south of Dutchess County) in the fall , as well (Levine 1998).
J F M A M J J A S O N D
Present Breeding
The time of year you would expect to find Forster's Tern present (blue shading) and breeding (orange shading) in New York.
Similar Species
  • Common Tern (Sterna hirundo)
    Common Terns appear similar to Forster's Terns but have shorter legs, longer wings, and a smaller head. The back is also medium grey compared to the light grey back of the Forster's Tern.
  • Roseate Tern (Sterna dougallii)
    Roseate Terns appear similar to Forster's Terns but have a bill that is mostly black with red-orange at the base and reddish-orange feet. The wingbeat of the Forster's Tern is much slower than that of the Roseate Tern (National Geographic Society 1999).