The Drongos of this genus are among the commonest of Indian birds, one or other of the species being found in every part of the country which is open or cultivated, and even in forest.
The various species of Drongos are not easily separable, except when large series of each are available for examination side by side. With the numerous specimens in the British Museum, the majority of which came from the Tweeddale and Hume Collections, I have been able to establish eight species which occur within my limits.
I am unable to find any characters by which the genus Buchanga can be separated from Dicrurus. The former is said to have a more deeply forked tail; but this feature cannot be regarded as of generic value, for it varies in all the species of this genus, and is a matter of degree only. I have therefore united the two genera.
Taking the eight species, it is easy at once to separate two from all the others by their perfectly black plumage, and from each other by the extent to which the tail is forked. These two species present no difficulty, and no one has seriously proposed to subdivide either of them into two or more races so far as Indian specimens are concerned. The African species or race D. assimilis need not be discussed here.
Another species, D. leucogenys, is also an easily recognizable one, having the sides of the head white. Very young birds might be confused with the Grey Drongos, presently to be noticed, were it not that they have the lores white or whitish, whereas the Grey Drongos have the lores dark brown or black. If D. intermedius, Blyth, recorded from Penang, was really killed at that place, and was not imported into it and subsequently re-exported to Calcutta (where it came under Blyth's notice), it must have been a young D. leucogenys. No other species of Dicrurus is known to occur in the Malay peninsula, at least near Penang. Blyth's title is too doubtful to be applied to any species.
Next come three species which may be termed Ashy or Grey Drongos. No two authors agree about these birds, and unanimous agreement regarding them will probably never be reached. In my opinion there are three distinct species in India and Burma, and no more. The differences in the shade of colour and in size in these species are correlated with different areas of Distribution. There is, first, D. longicaudatus, which is found from the Hima¬layas to Ceylon and east to the Brahmaputra river. The upper plumage of this bird may be termed metallic indigo, and the lower a dark grey. South of the Brahmaputra, extending to Lower Pegu and Northern Tenasserim, the foregoing species is replaced by a bird the upper plumage of which may be termed bluish grey and the lower ashy grey. This bird is also found in Java, Lombock, and Palawan, and is the Edolius cineraceus of Horsfield. All Hodgson's birds in the British Museum are the dark continental species D. longicaudatus, and were killed in Nepal or Sikhim, and consequently his name (D. pyrrhops) cannot be applied to this pale Burmese species, even if a name were required for it, which fortunately is not the case. The third species is a dark bird inhabiting portions of Lower Pegu, all Tenasserim, and the Malay peninsula, as far south as Junk Ceylon. Its upper plumage may be termed deep ashy indigo and the lower dark grey. This bird has never received a name ; it appears to he the Buchanga leucophaea of Vieillot apud Hume. The Dicrurus leucophaeus of Vieillot is, however, in my opinion, a bird which can never be satisfactorily determined, and the continued use of the name can only lead to confusion.
There remain two species which are characterized by the presence of a considerable amount of pure white on the lower plumage. This character will suffice to separate them from all the other Dicruri. They may be separated from each other, not so much by the amount of white on the lower parts as by the colour of the throat and breast and the upper plumage.
In Dicrurus the bill is stout, sharply carinated, and covered at the base by thick-set feathers, which partially conceal the nostrils. There is no crest or tuft on the head. The tail is well forked, the outermost feather exceeding the middle pair by a distance of from one to two and a half times the Length of the tarsus. The outer tail-feathers have a slight curl upwards.
Key to the Species.
a. Entire plumage deep glossy black; the lower plumage sometimes mixed with white.
a1. Outermost tail-feather exceeding middle pair by a distance about equal to tarsus……………D. annectens, p. 312.
b1. Outermost tail-feather exceeding middle pair by a distance greater than twice
tarsus……………D. ater, p. 312.
b. Upper plumage deep indigo.
c1. Lower plumage uniform dark grey.
a2. Outermost tail-feather exceeding middle pair by more than 2 inches; Length of tail 5.5 to 7 inches……………D. longicaudatus, p. 314.
b2. Outermost tail-feather exceeding middle pair by much less than 2 inches; Length of tail 4.9 to 5.5 inches……………D. nigrescens, p. 315.
d1. Lower plumage partially white.
c2. Throat and breast grey……………D. caerulescens, p. 316.
d2. Throat and breast dark brown……………D. leucopygialis, p. 316.
c. Upper plumage bluish grey.
e1. Lores or whole side of head white or whitish……………D. leucogenys, p. 317.
f1. Lores blackish; sides of head similar to upper plumage……………D. cineraceus, p. 318.