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Black-throated Diver in breeding plumage has ashy-grey upper-head and neck; mantle is black with purple and green tinge and with rows of white spots; throat and upper part of fore-neck are black with green and purple tinges; there is row of white spots on throat; and white strips on neck-flanks; flanks are black; upperparts including axillaries are white. Bill is black; legs are black in outer parts and bluish-grey in inner ones. Eyes are red-brownish. In winter plumage upperparts are black-brownish; underparts including cheeks and feathers of neck are white; upperhead and rear-neck are grey. Juveniles have plumage as on winter adults, but more dingy. Sizes: wing 290-350 mm, tail 54-62 mm, tarsus 80-83 mm, bill 58-70 mm.

Distribution

All Siberia. Now relatively common in tundra (including in mountains), forest-tundra, and only locally in taiga and forest-steppe. In th most part of range extinct or became rare.
Two subspecies:
G.a.arctica - west from the Baikal area and the Lena River water catchment; upper head and hindneck lighter, black patch on foreneck with violet glance);
G.a.viridigularis - east from the same area (upper head and hindneck darker, black patch on foreneck with green glance). Probably the eastern subspecies will be split to two ones i.o. northrn and southern.

Biology

Black-throated Diver is rare breeding migrant. Spring occurrence end April – late May. Nesting on large reservoirs with surface vegetation in forest-steppe, steppe and on mountain taiga lakes. Breeds in separate pairs at 0.5-1.5 km from each other. Nest is built along the shores of lakes or on old floating vegetation in reservoirs from dry reed stems and leaves; sometimes eggs laid in shallow hole in wet ground. Clutches 2, rarely 3 eggs in mid-May - end of June. Incubation lasts 28 days. Often a brood consists of only one nestling. Juveniles recorded from end May to mid-September. Autumn migration singly and in flocks of up to 7 birds from second half of September before reservoirs freeze (generally to mid-October – early November).