PREFATORY LETTER. 



The present report, which has been prepared by Prof. W. W. Cooke, 

 with the assistance of Mr. Otto Widinann and Prof. D. E. Lantz, is the 

 first fruit of the co-operative labors of the Division of Economic Or- 

 nithology of the Department of Agriculture and the Committee on 

 Bird Migration of the American Ornithologists' Union. It consists of 

 two parts: (1) an introductory portion treating of the history and 

 methods of the work, together with a general study of the subject of 

 Bird Migration, including the influence of the weather upon the move- 

 ments of birds, the progression of bird waves and causes affecting the 

 same, the influence of topography and altitude upon migration, and the 

 rates of flight in the various species ; and (2) a systematic portion in 

 which the five hundred and sixty species of birds known to occur in the 

 Mississippi Valley are treated serially, the movements of each during 

 the seasons of 1884 and 1885 being traced with as much exactness as 

 the records furnished by the one hundred and seventy (observers in the 

 district permit. 



The chapters entitled "The Eelation of Migration to Barometric Press- 

 ure and Temperature," and "A Study of the Bird Waves which passed 

 up the Mississippi Yalley during the Spring of 1884," are worthy of the 

 most careful perusal; and the articles on the Kingbird and Purple 

 Martin, in the systematic portion of the report, are particularly in- 

 structive. Indeed, I feel no hesitancy in expressing the belief that the 

 present report is the most valuable contribution ever made to the sub- 

 ject of Bird Migration. 



For the opinions herein expressed, relating to the theoretical questions 

 involved in the study of Bird Migration, Professor Cooke alone is re- 

 sponsible. Some of these opinions are diametrically opposed to those 

 held by the editor, but in a few instances only has the editor taken the 

 liberty to add his views on the subject ; in all such cases the interpo- 

 lated remarks will be found in bracketed foot notes, over his initials. 

 In fact, it has not been thought proper to make any changes in the First 

 Part of the report, save the verbal alterations necessary in preparing it 

 for the press. In the Second Part, or " Systematic Eeport," the case is 

 entirely different, for this portion of the report deals with fact instead 

 of theory. Here the editor has deemed it his duty to make the subject- 

 matter conform to the present state of knowledge on the subject. With 



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