The Red-flanked Bluetail, or Tarsiger cyanurus, is a diminutive passerine, a jewel of the forest, with a length of 13-14 cm and a weight of 10-18 grams. It is a bird of striking contrasts: the male sports a deep blue upperpart and the characteristic blue tail and rump, while the female and immature males are more subdued with brown upperparts, yet still share the vivid blue rump and tail. Both sexes boast orange-red flanks, a white throat, and greyish-white underparts, with a small, thin black bill and slender black legs completing their delicate appearance.
When identifying the Red-flanked Bluetail, look for the blue tail and rump, and the orange-red flanks that are the hallmark of both sexes. The male's dark blue upperparts are distinctive, whereas females and immature males are more cryptically colored with brown. Their slim build and size are comparable to the common redstart, but slightly smaller than the European robin.
This species favors mixed coniferous forests with rich undergrowth, where it breeds across northern Asia and northeastern Europe, from Finland to Kamchatka, and south to Japan.
The Red-flanked Bluetail is a migratory bird, wintering in southeastern Asia, including the Indian Subcontinent, the Himalayas, Taiwan, and northern Indochina. Its breeding range is gradually extending westward through Finland, and it is an occasional vagrant to Western Europe and North America.
The Red-flanked Bluetail exhibits behavior akin to the common redstart, often seen flicking its tail and darting from perches to snatch insects mid-air or from the ground. The male is known to deliver its melancholy trill from the treetops.
The male's song is a melancholy trill, while the call of this species is a characteristic chat "tacc" noise, a sound that punctuates the stillness of its forest habitat.
Nests are constructed on or near the ground, where the female incubates a clutch of 3-5 eggs, a testament to the continuation of the species amidst the forest floor's leaf litter.
The Red-flanked Bluetail can be confused with the common redstart due to size and behavior, but the blue tail and rump are distinctive identifiers. The European robin is also similar in size but lacks the blue and orange-red coloration.
As an insectivorous bird, the Red-flanked Bluetail feeds on a variety of insects, which it catches with agility in flight or on the ground.
The IUCN Red List currently classifies the Red-flanked Bluetail as Least Concern, indicating a stable population across its wide range.