Sterna longipennis Nordmann, in Erman's Reise (1835), 17;
Saunders, Cat. Birds Brit. Mus. (1896), 25, 67; Blanford, Fauna
Brit. Ind. Bds. (1898), 4, 319; Sharpe, Hand-List (1899), 1, 135;
Oates, Cat. Birds' Eggs (1901), 1, 185, pl. 14, fig. 4.
Basilan Straits (Mearns). Eastern Siberia, Kamtchatka, and Japan;
in winter China to New Guinea.
"Coloration.--Similar to that of S. fluviatilis [= hirundo], except
that the bill is always black and the feet are blackish. Adults are
darker in color, both above and below, but the difference is not
great. All the measurements appear identical, or nearly so, except
those of the bill, which is altogether smaller, and measures about
45 mm. from the gape." (Blanford.)
"Adult in winter.--Forehead flecked with white otherwise similar.
"Immature.--Like that of fluviatilis [= hirundo] from which it
can hardly be distinguished except by the color of the bill and
feet and the somewhat smaller size and more delicate shape of the
latter." (Saunders.)