232 FROM BLOMIDON TO SMOKY. 



the ground, in a cup-shaped hollow in a birch 

 stump. It is evident that a species which varies 

 the location of its home as widely as this must 

 contain individuals which have their power of 

 selection highly developed. The kingfisher's in- 

 stinct takes him to a gravel bank, in the face of 

 which he digs a hole. He is satisfied with one 

 set of conditions, and those conditions are simple 

 in kind. The song sparrow, which builds in a 

 hollow willow, or in a depression in a high stump, 

 has not been satisfied with simple conditions, but 

 has exercised her power of selection to a remark- 

 able degree in finally choosing very unusual sur- 

 roundings for her home. 



Much as birds of a species resemble one an- 

 other, every collecting ornithologist knows how 

 rare it is to find two individuals whose colora- 

 tion and measurements correspond exactly. In 

 series containing hundreds of specimens of the 

 same species, it is almost impossible to find two 

 skins which agree so closely as to be indistin- 

 guishable. Moreover, in such extended series, 

 it is common to find specimens which vary in a 

 radical way from the average. Not only does 

 albinism occur, but other unusual features ap- 

 pear in color and form in a way to suggest rever- 

 sion to some earlier stage in the development of 

 the species. For example, I have seen several 

 specimens of the cedar bird which had white 



