156 Henshaw on Melospiza meloda and its Allies. 



The Song Sparrow, althovigh 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 

 tlii'oughout 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. Coues 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. mdodn, and of all the forms into which 

 the species subdivides, except perhaps insigais, this appears to be 

 the most constant in the maintenance of its peculiarities over its 

 wide habitat. So fiir as color goes, the variation appears to be 

 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- 



