How BIRDS ARE NAMED 



we learn something of the influences which create species. Thus, climate 

 has been definitely proven so to alter a species, both in size and color that, 

 as we have seen in the case of the Song Sparrows, marked climate changes 

 are accompanied by correspondingly marked changes in the appearance of 

 certain animals. In naming these animals we are, in effect, giving a 'handle 

 to the fact' of their evolution by environment. 



Since it is evident that a bird may vary much or little, according to the 

 governing conditions and its tendency to respond to them, no fixed rule can 

 be laid down which shall decide just what degree of difference are deserv- 

 ing a name. It follows, therefore, that in some cases ornithologists do not 

 agree upon a bird's claim to subspecific rank. 



In North America, however, questions of this kind are referred to a 

 committee of seven experts of the American Ornithologists' Union, and 

 their decision establishes a nomenclature, which is accepted as the standard 

 by other American ornithologists and which has been adopted in this volume. 



Foreign birds of wholly accidental occurrence, most of which have been 

 found in North America but once or twice, are included in the systematic 

 list of North American birds, but are not described or figured in the body 

 of the book, where their presence would tend to convey an erroneous im- 

 pression of their North American status. Furthermore, records of the 

 presence of birds so rare as these can be properly based on only the capture 

 of specimens. 



In the preparation of the following pages both author and artist have 

 had full access to the collections of the American Museum of Natural 

 History, and they are also glad to acknowledge their indebtedness to 

 William Brewster of Cambridge, Massachusetts, to Robert Ridgway, Curator 

 of Birds in the United States National Museum, and to C. Hart Merriam, 

 Chief of the Biologic Survey, for the loan of specimens for description and 

 illustration. 



