Key to Subspecies.
A. White on tail less in extent and suffused with fulvous………..C. a. acutirostris, p. 327.
B. White on tail more in extent and purer in colour………..C. a. tibetana, p. 328.
It is with considerable hesitation that I keep these two races distinct but Osmaston's specimens obtained in Ladakh off their nests and one similarly collected by Ward certainly do have less, and less pure, white upon their outer tail-feathers than have other specimens sent to me with nests and eggs from Tibet. There is a great extent of variation in individuals and much overlapping, so that more breeding birds are required to either confirm or refute the separation of C. acutirostris into two races.