PEEFACE. 



The present paper has been written more with the 

 hope of stimulating thought and inciting research in a 

 new and as yet almost untrodden field of ornithological 

 inquiry, than with the expectation of reaching definite 

 results. The subject is as yet too new and difficult to 

 be reduced to even the semblance of an exact science, 

 and accordingly all the views here set forth are more or 

 less provisional and tentative. I have constantly pro- 

 ceeded upon the. assumption that a poor theory is better 

 than no theory, provided it be not considered as final, 

 since it affords an opening wedge for the further study of 

 a subject. Accordingly many of the views here set forth 

 are hardly to be considered as more than guesses, and it 

 is expected that future study will serve to show their 

 fallacy. If they lead to this further study, however, 

 and to more exact and comprehensive work by others, I 

 shall be glad to see them overturned and their places 

 filled by more worthy hypotheses. 



In the preparation of the work I have received much 

 valuable assistance, which I here take pleasure in ac- 

 knowledging. Much of the examination of specimens 

 was done at the United States National Museum, the 

 authorities of which kindly placed their collection of 

 birds at my disposal. To Mr. Robert Ridgway I am in- 

 debted for innumerable personal favors during my stay 

 in Washington. His Manual of North American Birds 

 has formed the systematic basis for this paper. Dr. L. 



