Page:The Fauna of British India, including Ceylon and Burma (Birds Vol 1).djvu/426

382 with black ear-coverts to the pale eastern forms with almost white ear-coverts. At the same time, all along the joining line of Molpastes h. burmanicus, M. h. nigripileus and M. h. bengalensis on the West with M. h. chrysorrhoides on the East we have not only many intermediate birds, which might equally well be assigned to either form, but there are many birds, the majority in fact, which can quite definitely be credited to one or the other. Thus there are in the British Museum Collection specimens from the Shan States, Yunnan, Siam, Karenni, Tenasserim, etc., some of which are labelled chrysorrhoides, some nigripileus, some atricapillus and some klossi but of the birds so labelled there are many of which it is impossible to say to which race they belong. Davison, Armstrong and others obtained birds at the same place about the same date which they had no difficulty in calling chrysorrhoides or nigripileus, yet others again are referable to either. It appears to me that all along the Siam–Burmese boundaries there is a narrow region in which there is no stable form found and where, evidently, there are such conflicting conditions in the environment that Nature has not yet had time to evolve one definite form. It is, of course, true that in all lines of demarcation between geographical races intermediate forms are the rule but in this intervening territory intermediate individuals are less common than such as can be definitely assigned to one or the other of the races in the adjoining area.

In view of the many individuals which are exactly half-way between chrysorrhoides and their next-door neighbours, I propose in this work to treat all the forms as geographical races of hæmorrhous.

Molpastes chrysorrhoides klossi Robinson, Bull. B. O. C., xli, p. 12 (1921) does not seem to be maintainable; the Museum series varies in wing measurements between 87 and 104 mm., whilst the very large series of Chinese birds range from 90 to 107 mm., one huge bird from Amoy having a wing of 111 mm. On the other hand, it is quite possible that the birds of West Siam may be separable as somewhat smaller and darker on an average. The series in the British Museum from that country is insufficient to determine this point.

Key to Species and Subspecies.