The Amount of Overlap Allowable for Subspecies

THE present tendency toward finer and finer subdividing of species into subspecies or geographical races, with formal trinomial nomenclature, is regarded from different viewpoints, both approving and disapproving. Agreement or at least a clarification of the principles to be followed in the applying of subspecific names is to be hoped for. The present paper is a contribution toward the clarification and stabilization of taxonomic practice in regard to lightly defined subspecies. VARIATION IN THE SPECIES Every individual bird differs somewhat from every other bird; any local population is at least slightly different from any other, while in appearance some populations differ widely from others of the same species. These different degrees of variation are illustrated by such examples as the introduced House Sparrow, Passer domesticus, in North America in which Lack (1940) found very little geographical variation (Calhoun's (1947) study on the same subject produced more positive results, but his methods do not inspire confidence); the Lincoln's Sparrow, Melospiza lincolnii, in which, within the named subspecies, there is much geographical variation below the level at which it is useful to name further races (Miller and McCabe, 1935); the Field Sparrow, Spizella pusilla, in which a distinct eastern and western race occupy considerable areas with a broad area of intergradation between (Wetmore, 1939: 240), and such complexes as that of the Sapsucker, Sphyrapicus varius, in which some students still prefer to retain the three very distinct types as species.