Black-backed Forktail

识别特征

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.<p>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 tail has a white tip and three white bands created by the ends of shorter tail feathers. The beak of the species is black, while the feet and legs are whitish-pink or a light flesh colour. The iris is brown or dark brown.<p>The black-backed forktail does not exhibit sexual dimorphism, and has no known geographic variation in its appearance. Nothing is known of its moulting. Juveniles of the species lack the prominent white stripe across the forehead, and the areas that are black on the adult are sooty brown or dull black. Juveniles have a white spot behind the eye, and may have dark scales or speckles on its flanks, breast, and belly. The tail of the juvenile is usually shorter, while the mandible is yellowish, and the maxilla have whitish cutting edges.<p>The bird is similar to the slaty-backed forktail, but lacks the slaty back of the latter, and is also smaller in size. It also has a slimmer bill. The white band on its face is narrower than that of the otherwise similar white-crowned forktail: it is also distinguished by its white, rather than black, breast. Field identification guides describe it as being the same size as bulbul species. Its call is described as a short and whistled "tseep - dew" or "hurt-zeee". The two syllables of this call are sometimes produced separately, as a hollow "huu" and a shrill "zeee", which are somewhat higher pitched than the call of the slaty-backed forktail. It produces a two syllable call when disturbed. It also makes a call similar to that of the slaty-backed forktail, described as being reminiscent of a squeaky hinge. It has been described as occasionally producing a short song as well.

分类信息

British naturalist Brian H. Hodgson scientifically described the black-backed forktail in 1836, from a specimen obtained in Nepal. It was originally placed in a new subgenus Enicurus in the genus Motacilla, which contains the wagtails. Hodgson described the species as sharing the characteristics of the genera Motacilla and Turdus, having an intermediate morphology, a general shape closer to that of Turdus species, and behavior closer to that of Motacilla. The species is currently placed within the family Muscicapidae, which includes Old World flycatchers and chats. The species has been referred to as the black-throated forktail.

学名

Enicurus immaculatus

命名信息

(Hodgson, 1836)

目

Passeriformes

科

Muscicapidae

属

Enicurus

分布与栖息地

迁徙

Resident species

行为

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.<p>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. The eggs have been recorded as averaging 2.08 centimetres (7⁄8 in) in length and 1.58 centimetres (5⁄8 in) in width. Both male and female birds participate in the construction of the nest and in incubation. Though the species is largely sedentary, first-year birds disperse from their parental breeding areas between April and October.

保护状况

种群趋势

stable