Note that the taxon cumatilis, which was formerly considered conspecific with Cyanoptila cyanomelana, is now treated as a separate monotypic species Zappey's Flycatcher Cyanoptila cumatilis.
Cyanoptila cyanomelana is now considered to have two subspecies:
C. c. cyanomelana breeding in Japan and the southern Kuril Islands.
C. c. intermedia breeding in northeast China (Heilongjiang south to eastern Hebei), southeast Russia (Amurskaya Oblast and Primorskiy Kray) and the Korean peninsula.
Note also that the name cumatilis was previously incorrectly ascribed to the population now known as intermedia.
On present knowledge it is not possible to safely separate females and most immatures of C. cyanomelana and C. cumatilis away from the breeding grounds and out of the breeding season. Photographs of which we cannot separate birds are retained here for convenience and reference.
Leader, P.J., & Carey, G.J. (2012), Zappey's Flycatcher Cyanoptila cumatilis, a forgotten Chinese breeding endemic, Forktail 28: 121-128.