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23â€“28 cm (9-11 in)
The two subspecies are very similar in breeding plumage; the most useful distinction is that the underwing of C. n. niger is dusky grey, while the underwing of C. n. surinamensis is white.
In winter and juvenile plumages, both have a white underwing, but the head and flank patters differ more obviously; C. n. niger has a sharply defined black crown, a narrow black 'peg' on the side of the neck, and white flanks, while C. n. surinamensis has a diffusely defined grey rear crown, a broad, diffuse grey-brown 'peg' on the side of the neck, and dusky grey flanks (see photos, right, for comparison).
 Similar species
See White-winged Tern for differences.
Breeds in wetlands in central and eastern Europe, western Asia, and central North America. Winters mainly at sea, also on larger lakes and rivers, on the west coast of Africa and both coasts of Central America and northern South America.
There are two subspecies:
A few authors have suggested they might be better treated as separate species, but none of the major authorities have taken this up at the moment.
Freshwater lakes, gravel pits and reservoirs, marshes, wet grassland; in winter on sea coasts and estuaries, and occasionally large lakes.
The diet includes insects, invertebrates and small fish.
The nest is usually floating vegetation in shallow water (possibly on the ground close to water). The clutch consists of 2-4 eggs which are incubated for 21-22 days. The young fledge after 19-25 days.
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