PREFATORY LETTER. 
The present report, which has been prepared by Prof. W. W. Cooke, 
with the assistance of Mr. Otto Widmann and Prof. D. E. Lantz, is the 
first fruit of the co-operative labors of the Division of Economie 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 c-bservers in the 
district permit. 
The chapters entitled “‘The Relation of Migration to Barometric Press- 
ure and Temperature,” and “A Study of the Bird Waves which passed 
up the Mississippi Valley 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 Report,” 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 
5 
