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Species
Sterna sumatrana Raffles, 1822
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SUMMARY
Adults are largely white, with: a very pale-grey back, rump and uppertail-coverts and upperwings; a bold, black band extending from the lores, where narrow, across the nape; and a thin blackish outer web to the outermost primary, forming a dark leading edge to the outerwing in flight and to a dark lower edge to the folded wing. The underparts can have a faint pinkish tinge at times. The bill, legs and feet are black, and the eyes dark brown. Juveniles are similar to adults but with a less clear-cut black nape-band, and with dark mottling and wash to the crown; and dark crescents and white scaling to the saddle and tertials, extending diffusely onto the rear upperbody. The tail has fine dark edges and is less deeply forked than in the adult, and the upperwing is also scaled with black and marked with dusky cubital and secondary bars. The bill is black with a paler base, but the bare parts are otherwise like those of the adult. Black-naped Terns are often gregarious, especially when they are breeding and roosting, although less so when they are foraging. They occur in groups ranging from a few birds up to approximately 100. They are often seen standing with Crested Terns (Thalasseus bergii), Lesser Crested Terns (T. bengalensis), Bridled Terns (Onychoprion anaethetus = Sterna anaethetus) and Roseate Terns (Sterna dougallii), in large mixed groups, though there tends to be some segregation in these congregations. Black-naped Terns are more likely to land near a group of terns (even another species) than where there are no terns. They often forage with other species of terns and noddies, such as Bridled and Roseate Terns and Black Noddies (Anous minutus). However, during the breeding season, they forage singly.