Subspecies
Subspecies pallens and magnus intergrade in Yakutsk area, and these populations sometimes separated as subspecies jakutorum. Nominate and pallens intergrade in western Asia.
Proposed subspecies sibiricus included within pallens. Subspecies poikila of Spotted Owlet (Athene brama) apparently refers to this species.
The following 7 subspecies are recognised:
funereus (Linnaeus, 1758) - Europe from northern Scandinavia south to Pyrenees and then east to Urals, excluding Caucasus.
caucasicus (Buturlin, 1907) - Caucasus; possibly this race or nominate in northern Turkey.
pallens (Schalow, 1908) - Western Siberia, Tien Shan, and southern Siberia east through north-eastern China (Heilongjiang) to Russian Far East (including Sakhalin).
magnus (Buturlin, 1907) - North-eastern Siberia, from Kolyma to Kamchatka.
beickianus Stresemann, 1928 - North-western India (Lahul) and western China (Qinghai).
richardsoni (Bonaparte, 1838) - North America (from central Alaska south to western USA, and east through Canada to Labrador).
The Reader's Digest Book of British Birds 1980, 3rd Edition, Drive Publications Ltd ISBN 0 340 25308 8
Birds in Colour Campbell, B., 1960, Penguin Books Ltd
The Pocket Guide to Nest and Eggs Fitter, R.S.R., 1954, Collins
RSPB Handbook of British Birds Holden, P., Cleeves, T., 2002, A & C Black ISBN 0 7136 5713 8
Birds of Britain and Europe Sterry, P., et al., 2001, AA Publishing ISBN 0 7495 3068 5
The Popular Handbook of British Birds Hollom, P.A.D., 1973, H.F. & G. Witherby Ltd ISBN 0 85493 002 7
BirdLife International Species Factsheet