6 
direction, forms the successive steps by which present-day evolutionists 
explain the origin of new species. Individual variation, however, is dis- 
regarded in classification unless it has proceeded far enough to produce 
marked and constant differentiation over a definable natural group of a 
species. 
Geographical variation may be regarded as the result of a common 
tendency to individual variation acting over a whole community of individ- 
uals tending towards a common goal, and is held to be induced and directed by 
local olimatie and other conditions. Thus in many cases we find that within a 
widespread species all individuals inhabiting certain localities have character- 
istics that separate them from those of the surrounding areas. Individuals 
in a dry desert country are apt to be smaller and lighter in coloration, 
whereas those in a warm, moist country are usually larger and darker. 
These differences are in some cases marked and obvious; in other cases they 
are so slight as to be noticeable only by comparing large numbers of speci- 
mens and can be detected only by averages. Thus there is every degree 
of differentiation, due to geographical habitat, from pronounced departures 
from type, of almost specific value, to the finest shades of differentiation 
that skilled specialists can distinguish and which are inappreciable to the 
ordinary eye. The outstanding fact, however, that prevents the most 
marked geographical variation from full specific standing, is that these 
minor forms intergrade so that in intermediate localities every shade of 
differentiation between the extremes can be found. Between species this 
gradual merging of character is not supposed to occur, and however fine 
the distinctions may be, the divisions should be sharp and defined. We, 
therefore, recognize these intergrading variations due to or based upon 
geographical distribution as Geographical Races, Varieties, or Subspecies, 
the last term being now the most usual, and we regard them as species in 
the making before the connecting stages binding them to the original 
stock have, owing to the increasing sterility between the variants, disappeared. 
Except in such rare cases of physical isolation, as where an oceanic island 
habitat precludes continuous distribution, we take, in practice, the exis- 
tence of intergrades as the evidence of subspecific status. Besides these 
divisions of taxonomic value there are a few other variants that, owing to 
their erratic occurrence, cannot be recognized in our classification. These are 
“Albinos,” “Melanos,” and “Dichromatic Forms.” 
GEOGRAPHICAL RACES 
Subspecific varieties are divisions of the species and, except in special 
lines of work, or where special exactitude is necessary, are of minor import- 
ance. As these subspecies are also in many cases based upon points of differ- 
ence perceptible to only the most experienced observers, they are mainly 
outside the sphere of interest of the average amateur observer. 
NOMENCLATURE 
Every North American bird has a common or vernacular name author- 
ized by usage and recognized by the leading ornithologists, and there is 
seldom necessity for the scientific nomenclature in ordinary use. How- 
ever, it is well for all who are interested in birds to familiarize themselves 
with as many of the scientific names as possible, as they are not only essent- 
ial in more advanced work but they are of practical use in grasping the 
