The Little Tern is a species which has been most difficult to divide into its various geographical races, principally because of its great propensity to wander far afield from its proper breeding-area, so that in the non-breeding season we may have two, three or even more races found together in one place. Hume divided his birds into species, subspecies at that time not being admitted, upon the colour of the shafts of the primaries, a very important characteristic, together with certain other features.
In Indian limits we appear to have five forms the typical S. a. albifrons, which is a casual straggler only into India in Winter; S. a. sinensis, a coastal breeding bird with an immense area stretching from Ceylon to Eastern China; S. a. pusilla, a river-breeding Tern found over most of India and Burma; S. a. saundersi, a very local form found over the Southern Red Sea and Persian Gulf to Sind and the Mekran coast and, finally, a fifth form which breeds in Mesopotamia, the Persian Gulf and Mekran, which, whilst most nearly allied to the European bird, is superficially very like saundersi.
Key to Subspecies.
A. Bill larger; culmen 28 to 34 mm.; much stouter.
a. First primary with pale brown shaft, second and sometimes third darker brown; rump
and upper tail-coverts quite white……………S. a. albifrons,[p. 135.
b. First primary with very white shaft, second and sometimes third with pale brown shafts; rump and upper tail-coverts almost white……………S. a. sinensis,[p. 136,
B. Bill smaller; culmen 26 to 32 mm.; much more slender.
c. First and second, and sometimes third primary with dark shafts; rump, upper tail-coverts and tail concolorous with grey of back……………S. a. praetermissa,[p. 138.
d. First primary with whity-brown shafts, second
a little darker; rump and upper tail-coverts almost concolorous with back……………S. a. pusilla,[p. 137.
e. First three primaries with black shafts; lump and upper tail-coverts concolorous with
back……………S. a. saundersi,[p. 138.
The distinctions given apply only to birds in full breeding plumage. It must, however, be remembered that birds wear the Winter plumage for a brief season only and that specimens in full Summer plumage may constantly be met with very far from their true breeding-haunts.