The Red-flanked Bluetail (Tarsiger cyanurus) is a small, vibrantly colored passerine bird found primarily in Asia and parts of Europe. Adult Red-flanked Bluetails typically measure around 5.5 to 6 inches in length, with a wingspan of approximately 8.5 to 9.5 inches. They weigh approximately 0.5 to 0.7 ounces. Distinguishing field marks include the striking blue tail and rump of males, which contrasts with their reddish-orange flanks and chestnut-colored sides. Females and juveniles have more subdued plumage, with less prominent coloration but still displaying hints of blue on the tail.

These birds are known for their migratory behavior. During the breeding season, Red-flanked Bluetails inhabit coniferous and mixed forests in northern regions, particularly in Siberia and parts of Europe. They build cup-shaped nests in dense vegetation close to the ground, using moss, leaves, and twigs. However, during the winter, they migrate to warmer climates, primarily in southern and southeastern Asia, including countries like Japan, China, and India.

Red-flanked Bluetails primarily feed on insects, spiders, and other invertebrates, which they forage for on the ground and occasionally glean from vegetation. They are adept at hopping among branches and foliage while hunting for prey. Their melodious and varied songs consist of trills, whistles, and warbles, adding to their charm and making them recognizable within their habitats.

The conservation status of the Red-flanked Bluetail is generally stable, but threats such as habitat loss due to deforestation and urbanization, as well as climate change affecting their breeding and wintering grounds, pose concerns for their populations. Preservation of their breeding and wintering habitats, along with efforts to reduce deforestation and protect forested areas, are crucial for the continued survival of these beautiful birds.

Birdwatchers and enthusiasts often travel long distances to catch a glimpse of the Red-flanked Bluetail during migration seasons. Their striking coloration, coupled with their unique migratory patterns, make them a sought-after sighting among birdwatchers, contributing to their allure in the world of avian enthusiasts.