Ottumwa tri-weekly courier. [volume] (Ottumwa, Iowa) 1903-1916, 1915-09-07
THE MYSTERY OF BIRD MIGRATION
in Bird Migration Goes Back to Remote Penod-Marvelous as We're the
Tales of Spring and Fall Movements of Birds as Tld by Early Observers
Yet Hardly Less Incredible Are the Ascerained Facts
BY w. w. COOKE.

ever collected in this country, and
permit broader and safer ~generaliza-
tons than have hitherto been possible.
For more than 1000 years the phe-
nomena Of bird migration have been
noted: but while the extent inc course
of the routes traversed have Of late
become better known, nc conclusive
answer has been found to the question,
why do North American birds migrate?
Two different and indeed Numerically
opposite theories have been advanced
to account for the beginnings of these
migrations.
According to the more commonly
accepted theory, ages g the United
States and Canada swarmed with nom
migratory bird life. long before the
Arctic Ice fields advancing south dur-
ing the glacial era rendered unin-
ha bitable the northern half of the
continent. The birds love of home
influenced them to remain near the
nesting site until the approaching ice
began for the first time to produce a
winter; that Is, a period Of inclement
weather which so reduced the food
supply as to compel the birds to move
or starve. AS the Ice approached very
gradually, HOW anu .tlcH IeCcOlIISS
these enforced retreats and absences
at first only a short distance and
for a brief time-increased both in
distance and duration until migration
became an integral part Of the very
being Of the bird. In other words, the
formation of the habit of migration
too place at the same time that
changing seasons in the year replaced
the continuous semi-tropical conditions
of the preglacial eras.
AS the ice advanced southwark the
swing to the north in spring migra-
ton was continually shortened and
the fall retreat to a suitable winter
h o m e correspondingly heightened,
until during the height Of the glacial
period birds were for he most part
confined to middle and South America.
But the habit Of migration had been
formed, and when the ice receded to-
ward it's present position the birds fol-
lowed it northward and in time es-
tablished their present long and
diversified migration routes.
Thus those who argue that love OF
birthplace is the actual impulse to
spring migration call attention to the
seeming Impotence of the earliest
migrants. Ducks and geese push north
ward with the beginnings Of open
water so early, so far, and so fast hat
many are caught by late storms and
wander d~isconsolately over frozen ponds
and rivers, preferring to risk starva-
ton rather than to retreat. The pur-
pie martins often arrive at their nest
ing boxes so prematurely that the cosy
home becomes a tomb if a sleet storm
sweeps their winged food from the air.
The b%luebirds' CHEEKY MARBLE we well
come as a harbinger Of spring, often
only to find later a lifeless body in
some shed or outbuilding where the
bird sought shelter rather than return
to the sunny land so recently left.
AS a matter of fact, however, only
a small percentage Of birds exhibit
these preseasonal migration propensi-
ties. The great majority remain in
the security of their winter homes
until spring is so far advanced that |
the journey can be made easily n
with comparatively slight danger; and
they reach the nesting spot when a
food supply is assured and all the con-
ditions Of weather and vegetation are
favorable for beginning Immediately
the rearing of a family of young.
If. however, a longing for home is
considered the main incentive to their
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