The Siberian Black-throated Diver.
Urinator arcticus suschkini Sarudny, Orn. Mitt., p. 111 (1912) (Russian Turkestan).
Vernacular names. None recorded.
Description. - Breeding plumage. Whole upper part of head, sides of upper neck and whole hind-neck dark grey; chin, throat and fore-neck black; a line of white streaks across the lower throat; a diagonal line down the side of the neck, almost joining the base of the hind-neck, of black and white streaks; upper plumage and wings black; a band down each side of the upper back of interrupted white bars; a similar broader band down the scapulars ; wing-coverts with two white subterminal spots; sides of upper breast and upper breast just next the black fore-neck streaked black and white ; axillaries and under wing-coverts white; flanks black; remainder of lower plumage white.
Colours of soft parts. "Iris red in adults, red-brown in young; bill in winter pale grey (juv. paler, more bluish-white), ridge of upper mandible blackish-slate, extending over sides to nostrils, tip horn-colour; bill in Summer blacker; legs and feet fad.) outside nearly black, inside very pale grey: webs same with flesh-coloured centres; (juv.) paler, outside dusky, inside milky blue-white." (Witherby for C. arcticus arcticus.)
Measurements. Wing 290 to 304 mm.; tarsus 67 to 72 mm.; tail 57 to 58 mm,; culmen 50 to 55 mm. There are few adult specimens of this race in the British Museum collection.
Winter plumage. Head not so pure a grey and becoming brown on the upper sides and the base of the neck; upper parts brown, becoming almost black on the lower back and the ends of the scapulars; wings only sparingly spotted with white; a few white spots on the scapulars showing where the bands come in Summer plumage; an indication of a brown line across the lower throat, sides of shoulders next to upper breast streaked brown and white; a black line across vent; rest of lower parts white.
Nestlings in down of C. a. arcticus are dark mouse-brown, the breast and abdomen paler or nearly white.
Young birds are more brown, less grey than adults; the feathers of the mantle have ashy-grey edges, which are obsolete or faint on the rump and upper tail-coverts ; sides of the neck more mottled and streaked brown than in the adults; black lines on the under tail-coverts more conspicuous and brown throat-line more definite.
Distribution. Breeding from the Urals to Lake Baikal and the Yenesei, Turkestan and the Kirghis Steppes.
This Diver has once been recorded in India, Mr. A. E. Jones having shot a young female on February 19th, 1922, on the Western Jumna Canal at Jagadhri, Ambala District, Punjab. Mr. Jones records the wing of this bird as only 290 mm., very small for this species and possibly that of a not fully-grown bird.
Nidification. I can find nothing on record about the nidification of this Diver but in a collection of eggs made by Emile Smirnoff in Siberia there are two eggs marked " Colymbus septrionalis, 27.7.21. Siberia, Trachansk, insula Dueson." These are much too big for the Red-throated Diver and are probably those of this race of the Black-throated Diver. They measure 82.1 x 51.4 mm. and 81.7 X 52.0 mm. Their colour is a dark brown and they are sparsely spotted and blotched with black and with a few secondary blotches of inky-grey.
Habits. Apparently similar to those of the Common Black-throated Diver. This latter Diver keeps much to small lochs and lakes in moors and heather-covered hills, feeds almost entirely on fish and is extremely shy and wary. The call is a loud, prolonged wail, audible at an immense distance, whilst they also have a hoarse croak of alarm.