156 Henshaw on Melospiza meloda and its Allies. 
The Song Sparrow, although apparently nowhere a permanent 
resident in the strictest meaning of the term, that is to the 
extent of the same individuals remaining in the same locality 
throughout the year, unless indeed insignis of the Alaskan islands 
furnish the exception, is yet migratory to but a limited extent, and 
it is probable that the change of locality with the migrations is in 
the instance of none of its forms at all marked. It is doubtless to 
this localization, with the ensuing constantly exerted influence of 
the same conditions of environment, that we are to attribute the 
extraordinary tendency in this bird to develop into races and 
offshoots, according as its range brings it under differing conditions. 
As Dr. Cones happily phrases it, “ Migration holds species true ; 
localization lets them slip.” And nowhere do we meet a better 
illustration of this aphorism than is presented by this Sparrow. 
A recent examination of the extremely large collection of Song 
Sparrows in the Smithsonian Institution, together with many others 
furnished by friends for comparison, has developed some facts that 
appear to be of sufficient value and interest to warrant brief men- 
tion. 
Here, as elsewhere, the variation through which the forms are 
indicated are of two kinds, viz. a variation in size, and also in colora- 
tion ; nor is it easy to say in which direction the change is most 
pronounced. 
The only Song Sparrow found in the Eastern United States, and 
which extends from the coast as far west as Nebraska and the 
Indian Territory, is the M. meloda , and of all the forms into which 
the species subdivides, except perhaps insignis , this appears to be 
the most constant in the maintenance of its peculiarities over its 
wide habitat. So far as color goes, the variation appears to he 
scarcely noticeable ; nor is the change in size very marked. Such 
as it is, it appears to bear out the general rule of an average in- 
crease of size to the northward. This law, it may be remarked 
here, appears to be equally applicable to all the other races. The 
general sameness in the topographical conditions of the eastern 
region, and the resulting similarity of climate, is doubtless the 
chief cause of the slight departure from type to be observed in 
meloda throughout its range. 
The Rocky Mountains, as far to the north as Oregon and to the 
south as our southern border, and the intermediate region west 
to the Sierras, are occupied by the var. fallax. This bird is dis- 
