the forster's tern (sterna forsteri) is a member of the tern family , sternidae .
the genus name sterna is derived from old english "stearn", "tern", and forsteri commemorates the naturalist johann reinhold forster .
it breeds inland in north america and winters south to the caribbean and northern south america .
this species is rare but annual in western europe , and has wintered in ireland and great britain on a number of occasions .
no european tern winters so far north .
this species breeds in colonies in marshes .
it nests in a ground scrape and lays three or more eggs .
like all white terns , it is fiercely defensive of its nest and young .
the forster's tern feeds by plunge-diving for fish , but will also hawk for insects in its breeding marshes .
it usually feeds from saline environments in winter , like most sterna terns .
it usually dives directly , and not from the "stepped-hover" favoured by the arctic tern .
the offering of fish by the male to the female is part of the courtship display .
this is a small tern , 3336 cm (1314 in) long with a 6470 cm (2528 in) wingspan .
it is most similar to the common tern .
it has pale grey upperparts and white underparts .
its legs are red and its bill is red , tipped with black .
in winter , the forehead becomes white and a characteristic black eye mask remains .
juvenile forster's terns are similar to the winter adult .
the call is a harsh noise like a black-headed gull .
this species is unlikely to be confused with the common tern in winter because of the black eye mask , but is much more similar in breeding plumage .
forster's has a grey centre to its white tail , and the upperwings are pure white , without the darker primary wedge of the common tern .
