Burrill, Bird Migration. 
101 
t 
ANON THE REASONS FOR BIRD MIGRATION: 
A FAVORITE FOOD THEORY. 
By A. C. Burrill. 
For many years the various attempts to explain the migration 
of North American birds has interested the writer, although no 
one seems to have arrived at a conclusion which all will accept. 
The theory of avoidance of extreme cold has been overturned by 
the fact that certain birds who have been proved to resist cold 
equal to the winter extremes, go south long before such cold 
weather arrives; the theory that the bird’s food suppiy is running 
short has been overturned by proof that the birds leave their 
northern nesting grounds before the actual food supply is any¬ 
where near exhausted; the theory that the birds seek the North 
for nesting purposes in order to avoid tropical enemies has been 
partly exploded by the presence of bird-destroying enemies in the 
North and the fact that many birds linger in the Northern regions 
months after breeding is over; and the theory of migration routes 
and instincts inherited from their time of origin during the Glacial 
Period is most seriously combatted by comparative psychologists—<■ 
who claim that a habit fails to persist for milleniums after the 
Original stimulus, viz., glacial conditions, is inoperative. 
An unprofessional opinion is that the reason of bird migra¬ 
tion has something to do with the food question together with the 
widespread habit throughout the animal kingdom of an inquisitive 
desire to wander or explore (Prof. N. S. Shaler, 1906, “Explora¬ 
tion,” Atlantic Monthly v. 97, No. 2 for Feb. pp. 145-156). 
In 1909, the writer suggested the need of studying bird phe¬ 
nomena connected with the flocking habit, especially flocking 
before migration (“Swallow Migration, 1909”, Bulletin of the 
Wisconsin Natural History Society, Vol 7, Nos. 3 and 4, page 
132, October, 1909). This was dwelt on at further length in the 
sketch on “Migrations of the Swallows and Other Birds” (in “By 
the Wayside,” Vol. 11, No. 6, pages 41-42, Dec. 1909), in which 
notes on some flocking points of red-winged black-birds in Wis¬ 
consin were included together with references to the literature on 
robin roosts. 
