kchaiyan

B. b. vulpinus has rufous uppertail with obvious dark subterminal band (adult) and no prominent dark carpal path as the patches are blended in dark  underwing coverts (than pale underwing coverts in japonicus, thus obvious carpal patches).

In Thailand, both ssp. (japonicus and vulpinus) occur, but it still remains unclear if an intergrade of vulpinus and japonicus (aka burmanicus at least, in Myanmar) also occur.