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Greater racket-tailed drongo
The greater racket-tailed drongo (''Dicrurus paradiseus'') is a medium-sized Asian bird which is distinctive in having elongated outer tail feathers with webbing restricted to the tips. They are placed along with other drongos in the family Dicruridae. They are conspicuous in the forest habitats often perching in the open and by attracting attention with a wide range of loud calls that include perfect imitations of many other birds. It has been suggested that these imitations may help in the formation of mixed-species foraging flocks, a feature seen in forest bird communities where many insect feeders forage together. These drongos will sometimes steal insect prey caught or disturbed by other foragers in the flock. They are diurnal but are active well before dawn and late at dusk. Owing to their widespread distribution and distinctive regional variation, they have become iconic examples of speciation by isolation and genetic drift.
==Description==
In most of its range in Asia, this is the largest of the drongo species and is readily identifiable by the distinctive tail rackets and the crest of curled feather that begin in front of the face above the beak and along the crown to varying extents according to the subspecies. The tail with twirled rackets is distinctive and in flight it can appear as if two large bees were chasing a black bird. In the eastern Himalayas the species can be confused with the lesser racket-tailed drongo, however the latter has flat rackets with the crest nearly absent.
This widespread species includes populations that have distinct variations and several subspecies have been named. The nominate form is found in southern India, mainly in forested areas of the Western Ghats and the adjoining hill forests of peninsular India. The subspecies in Sri Lanka is ''ceylonicus'' and is similar to the nominate form but slightly smaller. The subspecies found along the Himalayas is ''grandis'' and is the largest and has long glossy neck hackles. The Andaman Islands form ''otiosus'' has shorter neck hackles and the crest is highly reduced while the Nicobars Island form ''nicobariensis'' has a longer frontal crest and with smaller neck hackles than ''otiosus''.〔 The Sri Lanka drongo ''D. lophorinus'' used to be treated as a subspecies due to the suggestion that it formed hybrids with ''ceylonicus'' is considered a separate species in newer taxonomic treatments on the basis of their overlapping ranges.〔 Specimens of the nominate form have sometimes been confused with ''lophorinus''. Considerable variation in shape of the bill, extent of the crest, hackles and tail rackets exists in the island populations of Southeast Asia. The Bornean ''brachyphorus'' (=''insularis''), ''banguey'' of Banggai lack crests (''banguey'' has frontal feathers that arch forwards) while very reduced crests are found in ''microlophus'' (=''endomychus''; Natunas, Anambas and Tiomans) and ''platurus'' (Sumatra). A number of forms are known along the Southeast Asian islands and mainland including ''formosus'' (Java), ''hypoballus'' (Thailand), ''rangoonensis'' (northern Burma, central Indian populations were earlier included in this) and ''johni '' (Hainan).
Young birds are duller, and can lack a crest while moulting birds can lack the elongate tail streamers. The racket is formed by the inner web of the vane but appears to be on the outer web since the rachis has a twist just above the ''spatula''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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