178 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. YOL. 2. NO. 4-, 
I am aware that for the past decade, or a Httle more, there has 
been a tendency to attribute the causes of migration to the failure 
of food. It is still, however, a very general belief, especially with 
regard to the spring migration, that food is only a minor cause. 
Furthermore, I arn not aware that the causes of migration have 
ever received special treatment, hence have included a chapter on 
this subject. 
The remaining two chapters are the result of a method of 
investigation that has heretofore received very little application. 
The telescope offers a means for watching nocturnal migrants 
while they are in actual migratory motion. Though we gain a 
view of only an infinitesimal portion of the vast migratory wave 
in so small a field of vision, enough is revealed to make it well 
worth the undertaking. 
Since a great deal of the work on migration has been done in 
Europe, I have been unable to secure much of the valuable 
literature that I should have had. For such as I had access to 
I am indebted to Mr. H. Xehrling and ]\Ir. Paul Dernehl, both 
formerly of the Milwaukee Public ]^Iuseum. 
I wish especially to express my thanks to Dr. O. G. Libby 
for the abundant help he has given me and the interest he has 
•shown throughout the entire work. Also to Prof. Geo. C. Com- 
stock, of the Washburn Observatory, for the use of telescopes: 
One of three instruments — the finder on the large telescope, the 
students' telescope, or a large portable telescope — was at my con- 
tinual disposal. Other acknowledgments will be found in their 
respective places. 
CHAPTER I. 
HISTORICAL REVIEW. 
Xo one can doubt that the great semi-annual movement of the 
migratory birds must have been noticed and commented upon even 
from the earliest times. The Prophet Jeremiah refers to the 
appointed times of the stork. Anacreon wrote in his Thirtieth 
Ode, 
'•'Lovely s^vallo^v once a year. 
Pleased, you pay your visit here; 
When our elinie the sunbeani=^ sild 
Here your airy nest you build ; 
And when bright days cease to smile 
Fly to Memphis or the Nile." 
So far back as the times of Hesiod, we are informed that 
husbandrv was in great part regulated by the coming of the birds. 
It has been .stated that Persians and Arabs compiled portions of 
