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OFFICIAL ORGAN OF THE WISCONSIN, ILLINOIS AND MICHIGAN AUDUBON SOCIETIES 
One Year 25 Cents 
Single Copy 5 Cents 
VOL. XIV 
Published by the Wisconsin Audubon Society at (Madison, Wisconsin 
Entered as second class matter Auoust 23, 1909, at Madison, Wis., under the act of Congress of March 3, 1879 
APRIL, 1913 
NO. 8 
THE MIGRATION OF OUR BIRDS 
By F. H. King 
(Continued from March Number) 
] 
i. 
If we ask ourselves why so many birds 
make these long biennial flights, the im¬ 
mediate answer would be, they are im¬ 
pelled to do so by force of long estab¬ 
lished habit; then, if we ask how such a 
habit could have been fixed upon them, 
the answer must be, the habit was the 
outcome of an effort to live comfortably 
and prosper. Alfred R. Wallace ac¬ 
counts for the origin of this habit essen¬ 
tially in this way, and we are inclined to 
agree with him. The habit of wandering 
in search of food, common to all animals, 
has been exaggerated among birds, whose 
powers of locomotion are exceptional. 
Something like the incipient stage of 
this habit we see exhibited by our black¬ 
birds when they gather into flocks in 
the fall and move, in the morning, from 
the sloughs in which they were bred, out 
onto the prairies in quest of food, re¬ 
turning again toward sunset. Pigeons, 
too, have the same habit, and extend 
their flights in search of food over much 
greater distances than do the blackbirds. 
It is only a short time ago, speaking in 
units of geologic time, when the climatic 
conditions of Central Greenland pre¬ 
vailed over the North American conti¬ 
nent as far south as into Pennsylvania 
and Southern Ohio on the eastern side. 
This was an epoch of much lower mean 
annual temperature for Central and 
Southern North America, and the soil, 
deeply buried beneath glacial ice and 
snow, could have contributed no support 
to insect or seed-eating birds. Vegeta¬ 
tion may have been nearly or quite up 
to the front of the melting ice, as it is 
now in glacial regions, and here too we 
may believe certain species of birds were 
found during the summer. As this cold 
period faded insensibly into our warmer 
epoch, the ice front retreated at the same 
rate toward Greenland, closely pursued 
by the mantle of verdure. 
With the snow receding northward, 
and vegetation, with its accompanying 
insects, advancing at q, rate possibly 
much less than a mile in a century, the 
inevitable overflow of species from their 
natural breeding grounds would be more 
than likely to occupy the newly verdure- 
clothed territory as fast as reclaimed. 
But insect-eating birds could not survive 
during the winter in the newly occupied 
territory for want of food, and to fly in 
any other direction than southerly would 
fail to better their [conditions. Now 
such of these ice-frontier birds as did 
move southward on the approach of win¬ 
ter, would, as it passed into summer, find 
the climatic conditions unfavorable to 
them; but to escape from these would 
