I retain the four geographical races, assamica, marionae, affinis and microptera, as forms of this species. M. erythroptera has generally been accepted as a good species on account of the excessive amount of rufous on the primaries. This might be held to be of subspecific value only but that the area of the two forms would thus overlap. It is true that the extent of the rufous in the wing-quills varies greatly. Thus 31. a. affinis has more rufous than M. a. assamica, and M. a. marionae has more than M. a. microptera. On the other hand, none of these four ever have the rufous patches on the outer and inner web joining one another but always divided by a brown band running up the shaft. Both M. a. assamica and M. e. erythroptera breed n the same area in Western Bengal, Bihar, etc.
Key to Subspecies.
A. Upper parts ashy-brown with dark centres; no tinge of rufous on back………..M. a. assamica, p. 387.
B. Upper parts dark brown tinged with rufous………..M. a. marionae, p. 338.
C. Upper parts not very dark but very rufous
a. Wing over 78 mm………..M. a. affinis, p. 339.
b. Wing under 78 mm………..M. a. microptera, p. 340.