8O IN BIRD LAND. 
Allen’s valuable paper on the “ Origin of the In. 
stinct of Migration in Birds.’”’ ‘The extract is taken 
from an article by Frank M. Chapman, published in 
“The Auk” for January, 1894 : “ Nothing is doubtless 
more thoroughly established than that a warm tem- 
perate or sub-tropical climate prevailed down to the 
close of the Tertiary epoch, nearly to the Northern 
Pole, and that climate was previously everywhere so 
far equable that the necessity for migration can 
hardly be supposed to have existed. With the later 
refrigeration of the northern regions, bird life must 
have been crowded thence toward the tropics, and 
the struggle for life thereby greatly intensified. ‘The 
less yielding forms may have become extinct; those 
less sensitive to climatic change would seek to extend 
the boundaries of their range by a slight removal 
northward during the milder intervals of summer, 
only, however, to be forced back again by the recur- 
rence of winter. Such migration must have been at 
first ‘incipient and gradual,’ extending and _ strength- 
ening as the cold wave receded, and opened up a 
wider area within which existence in summer became 
possible. What was at first a forced migration 
would become habitual, and through the heredity 
of habit give rise to that wonderful faculty which 
we term the instinct of migration.” The reader’s 
attention is also directed to Mr. Chapman’s own 
article in the number of “ The Auk” indicated. 
It may be asked why some species remain in 
torrid and temperate climates, while others wing 
their way to the far north, even beyond the boun- 
Sa ee ee 
ST SY il A a A TE Ae a. AN. er iE ON tlh tg alt agi ———e 
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