Black-backed Forktail

A medium-sized forktail, the black-backed forktail is between 20.5 and 23 centimetres (8+1⁄8 and 9 in). It weighs between 25 and 29 grams. The length of the wing has been recorded as between 8.6 and 9.8 centimetres (3+3⁄8 and 3+7⁄8 in) in the male and 8.6 to 9.0 centimetres (3+3⁄8 to 3+1⁄2 in) in the female. The bill extends 2 centimetres (3⁄4 in) from the skull, while the tail is between 12.4 and 12.7 centimetres (4+7⁄8 and 5 in) long. The species has a broad white stripe beginning just behind the eyes and running across its forehead. The crown and mantle are completely covered in black feathering, which extends down to the upper forehead, face, scapulars, throat, and sides of the neck. The underparts of the bird are white, sharply delineated from the black of the throat. The lesser coverts and median coverts are completely black, as are the bases of the greater coverts. A broad white band runs across the wing, running across the greater coverts as well as the bases of the inner secondary and tertiary feathers. The highest tertial feather is white, and the inner primaries have white tips and the base of the secondaries are covered in a small white patch. The flight feathers are otherwise black. As with most other forktails, the tail of the species is long, graduated, and deeply forked. The feathers are black, with white tips, except for the outermost feathers, which are white. …

The black-backed forktail's habitat of choice is near fast-flowing rivers and streams in moist tropical broadleaf forest and subtropical lowland forest. It frequents rocks and boulders within or bordering streams, as well as mud or sand banks bordering rapidly moving stretches of water. The western end of the species's range is in Garhwal, in the northwest portion of the Indian state of Uttarakhand. The range extends from there through western and central Nepal to Bhutan and the northeastern Indian states, including Sikkim, Assam, Meghalaya, Arunachal Pradesh, Nagaland, and Manipur. It is known as a winter visitor to Nameri National Park in Assam. West of Sikkim the species is uncommon, but it is common in Bhutan. It is also found in the Sylhet and Chittagong regions of Bangladesh, where it is uncommon. The range extends to Myanmar, except for the region of Tenasserim, and to northwestern Thailand. It has also been reported from southwestern Yunnan in China, and from southeastern Tibet. Birdlife International maps its range as being contiguous over these regions, except for an area in south Myanmar separated from the rest of the range. Field guides for birds in south Asia describe its distribution as discontinuous. In the western part of its range the species is found up to 1,450 metres (4,760 ft) above sea level; in the eastern part, up to 900 metres (2,950 ft) above sea level. …

The species is solitary, or occasionally found in pairs, but may be seen in family groups during the breeding season. Described as a shy bird, it often bobs its tail when feeding, and when at rest opens and closes it with a scissor-like motion. It habitually flies along the course of a river or stream, and its flight is described as quick and straight, occasionally undulating slightly. It has been observed near waterfalls. The precise diet of the black-backed forktail is unknown, but it has been observed to consume aquatic insects, the larvae of these insects, and crustaceans. It typically forages along fast-moving streams and rivers, including on rocks in midstream, and may occasionally enter the water. It may also forage along slower-moving rivers, ponds, or forest pools, and has been recorded as foraging in damp areas of the forest. When inactive, it has been observed to remain in bushes or low shrubbery. The breeding season of the black-backed forktail is between March and June. The nest consists of a cup constructed of plant matter, including dried leaves, moss, and fibres, sometimes lined with leaf skeletons. It may be located in the hole of a dead tree, under a bank, on a ledge, or in a hole or cleft among rocks. Usually, three eggs are laid, which are pinkish and sparsely specked with fine red-brown. The speckles occasionally form blotches or caps at the end of the eggs. …