BULLETIN 
OF THE 
WISCONSIN NATURAL HISTORY SOCIETY. 
Vol. 2^ New Series OCTOBER^ 1902. No. 4. 
Exchanges should be mailed to the Wisconsin Natural History Society, in care 
of the Public Museum, Milwaukee, Wis. Communications should be addressed to 
the General Secretary. 
The Migration of Birds 
With Special Reference to Nocturnal Flight. 
H. A. WINKENWERDER. 
PREFATORY NOTE. 
During the fall of 1897 Dr. O. G. Libby called my attention to 
the excellent facilities the telescope offers for the study of bird 
migration, and upon his advice I took up the following work in 
the summer of 1899. It was intended that the paper should be 
complete in 1901, but owing to the pressure of other work and 
the amount of material collected this became impossible. 
Since so much in any one phase of the subject of migration 
depends upon a knowledge of the phenomena of the other phases, 
it becomes necessary to treat certain parts of the entire subject 
in order that the reader may obtain a clear understanding. The 
following Daper is consequently divided into four chapters, A 
Historical Review, The Causes of Migration, Migratory Routes, 
and The Manner of Migration. 
The reasons for presenting a historical review are (i) because 
I had the material on hand; (2) because the only paper of 'this 
nature in the English language, that of Dr. J. A. Palmen in the 
Smithsonian Report of 1892, deals only with the development 
of certain phases of the subject, and tells very little of the 'work 
done in America; (3) because it is an important adjunct to the 
rest of the paper. For much in this chapter I am indebted to 
Palmen's Ueber die Zugstrassen der Vogel. 
