“Adult male in breeding plumage.—Forehead, crown, and nape deep black; from the gape to the nape a conspicuous white streak; upper parts slate-gray, darker on the primaries, except when these are new and frosted; shafts white; inner webs of outer pairs of primaries white on the upper and greater part of the inner webs; upper tail-coverts gray; tail-feathers gray, with white outer webs to the outside pair; chin white or very pale gray; throat gray, darkening on the lower part; breast dark slate-gray, which deepens into black on abdomen and flanks; vent and under tail-coverts white; under wing-coverts white; axillars white with a faint tinge of gray. Bill blood-red; feet vermilion, drying to orange-color; webs deeply indented, but less so than in H. leucoptera. Length, 280; culmen, 35; wing, 235 to 241; tail, 96; tarsus, 23; middle toe with claw, 29.
“Indian birds, which are probably almost sedentary, are slightly smaller in size. Some of the birds resident in South Africa are of a distinctly darker hue both above and below than northern examples; Australian specimens, on the other hand, are inclined to be paler.
“Adult female.—Similar to the male, or a trifle paler in general tint.
“Adult in winter plumage.—Upper parts of a paler gray than in the breeding season; forehead white; crown and nape streaked and mottled with black; under parts entirely white; bill and feet reddish brown.
“Young in first plumage.—Crown and nape blackish brown, mantle mottled with brown and with warm cinnamon-brown edges to inner secondaries; tail slightly mottled and edged with ash-brown; the rest like the adult in winter. By December the brown markings are considerably diminished.
“Nestling.—Down at the base of bill black, forehead ruddy fawn-color; upper parts paler fawn, mottled and streaked with black; under parts white, except the throat, which is sooty black for a few days.” (Saunders.)
“Common about the Pasig River and Laguna de Bay. Several flocks were observed in Mindanao feeding over the paddy-fields.” (Bourns and Worcester MS.)
Genus STERNA Linnæus, 1758.
Bill much as in Hydrochelidon but somewhat longer; toes completely webbed; tail always distinctly forked; outer rectrices usually much longer than the others.