(585) Geocichla sibirica sibirica.
The Siberian Ground-Thrush.
Turdus sibiricus Pall., Reise Buss. Reichs, iii, p. 694 (1776) (Dauria). Geocichla sibirica. Blanf. & Oates, ii, p. 138.
Vernacular names. None recorded.
Description.— Adult male. Whole plumage deep slaty-blue black, the margins of the feathers a pale slaty blue and the outer three pairs of tail-feathers tipped with white; lores velvety black and a broad supercilium white ; the centre of the abdomen, vent and thigh-coverts white or mixed white and slaty grey; under tail-coverts broadly edged and tipped with white ; axillaries white tipped with blackish and under wing-coverts ashy black tipped with white.
Colours of soft parts. Iris dark brown; bill black; legs and feet greenish yellow to pale yellow or yellow-horny.
Measurements. Total length about 230 mm.; wing 114 to 124 mm.; tail 73 to 85 mm.; tarsus about 30 mm.; culmen about 20 mm.
Female. Whole upper plumage rich rufescent olive-brown, more rufous on the tail and edges of primaries; wing-coverts tipped with buff; a narrow supercilium, sides of head and ear-coverts mottled buff and dark brown ; lores and a streak from the gonys dark brown; chin and throat buff; breast bright pale rufous-buff tipped and edged with brown; lower breast white, similarly marked; centre of abdomen more or less white; flanks olive-brown barred faintly with darker brown; under tail-coverts white with broad brown marks on either side of the bases ; tail-feathers tipped with white on the three outer pairs ; axillaries white tipped with brown and under wing-coverts olive-brown tipped with white.
Colours of soft parts. Iris dark brown; bill dark horny-brown, the base of the lower mandible pale yellow; legs and feet orange-yellow.
Measurements as in the male.
Young male like the female but upper plumage as in male and the edges to the feathers below more slate-grey than brown.
Nestling. Brown above, tipped and centred on each feather with pale rufous-buff; below rufous broadly barred with black.
Distribution. Breeding in Central Siberia and wandering South in winter to India, Burma and Western China and there is a typical specimen in the British Museum collection from Sumatra. This race and the next very widely overlap in their winter quarters and there are many places in which both birds have been taken almost at the same time, as, for instance, Nwalabo in Southern Burma. There is seldom, however, any difficulty in assigning any individual to its proper subspecies. It has occurred as far west as Great Britain and France.
Nidification. Does not differ from that of the better known Japanese form, the next bird. In Central Siberia it breeds late in June between latitudes North 66° and 68°.
Habits. Similar to those of Davison's Ground-Thrush.