346 THE STORY OF A BIRD LOVER 



As a second suggestion, I believe that, with 

 the knowledge of individuals (for example, if you 

 become so conversant with a given number of 

 robins — say fifteen or twenty — as to know 

 them by their faces), you are in a position to be 

 able to examine the nature and extent of variation 

 of a kind that cannot be set down and formulated 

 in measure of exact dimension. For many years 

 a great deal of attention, care, and time has 

 been given to detailed measurements of different 

 parts of birds, as the wing, the beak, and the tail ; 

 but I am not aware that any one has given great 

 consideration or has had the opportunity to give 

 great consideration to the variation, for instance, 

 in expression, carriage, or song of different indi- 

 viduals. Traits of character, still more subtle, 

 which may best be described as mental, are, to say 

 the least, difficult to become acquainted with in 

 birds or other animals in a wild state. 



It is true that naturalists and ornithologists 

 understand pretty thoroughly that there is a cor- 

 relation in color with the sex or age, or with the 

 season of the year during which a kind of bird is 

 observed, and I think that most of us are aware 

 that there is a very wide variation in the intensity 

 and shade of color in at least some kinds of birds 

 which does not correlate apparently with any of 

 these several factors. It seems obvious that what- 

 ever changes occur in appearance which correlate 



