THE AUK: 



A QUARTERLY JOURNAL OF 



ORNITHOLOGY. 



vol. vii. January, 1890. No. 1. 



TO WHAT EXTENT IS IT PROFITABLE TO 

 RECOGNIZE GEOGRAPHICAL FORMS 

 AMONG NORTH AMERICAN 

 BIRDS ?* 



BY J. A. ALLEN. 



In the early thus of natural history minute differences of struc- 

 ture, size or color received little attention, and the groups looked 

 upon in early times as species now take, in not a few instances, 

 the rank of a genus, the one wide-ranging species of the early 

 authors having been found to include several species, each with 

 its own circumscribed habitat. Buffon, for example, considered 

 the exotic forms of life which closely resembled European types 

 either as being degenerate forms of the latter, or as slight modifi- 

 cations of them, due to climatic influences, differences of food, etc. 

 Even the species of Linnaeus, and of his contemporaries and 

 immediate followers, were often groups of a highly composite 

 character. It was not till much later that the importance of nicer 

 discriminations became apparent. 



By the middle of the present century the smallest appreciable 

 deviations b_ecame of specific import, and even a difference of 

 habitat was not unfrequently thought to be sufficient ground for 

 the presumption of specific diversity. Consequently individual 

 variations were unwittingly made the basis of specific distinctions. 



* Read at the Seventh Congress of the American Ornithologists' Union, Nov. 15, 1889. 



