Less than Sparrow. Old male of Red-flanked Bluetail is determined unmistakably by the grey-blue upperparts, especially bright on lesser wing coverts and upper tail coverts; the flanks are rusty. Differs from the Siberian Blue Robin by the rusty flanks. The autumn plumage is same color but the blue on the head and back is marked by olive-grey edges on feathers. In 2nd year male the coloration as in female: the tail is bluish, the rest of the upperparts are olive-gray, the flanks are rusty, narrow eye-ring is white, throat and belly are whitish, the breast is with unclear dark band. Some of the males has female-like color all their lives (grey-olive morph). Juveniles are like the juvenile Bluethroat or Robins, olive-brown pale mottled; but they are well distinguishable by the blue tail. Weight 12-18 gr, length about 12-15, wing 7.0-8.4, wingspan 21-24 cm.
Red-flanked Bluetail is rare, in places common breeding migrant, in most territory the rare passage migrant. Inhabits the coniferous taiga or the mix spruce-birch forests with the wet soil and the lot of wind-fallen branches; at attitudes 1200-2000 m; on migration visits the bush thickets on steppe rivers. In Siberia Bluetail builds the nest in the checks, cavities, between the roots, in tree holes, or between the moss stones, at 0.2-1.0 m from the ground; nest is built from the moss, dry grass and needles. Clutches 5-7 eggs. No nest in Kazakhstan was found. In spring appears in early June. In some places the singing males are registered every one hundred meters, but in other ones - after some kilometers only. The brood of well flying juveniles with adult birds recorded at July 2, 1972. On plains the migrated single birds were observed from the late September to the end of October.
