The semiannual movements of the yellow-billed loon present an unusual
problem in migration. It breeds along the Arctic coast, probably
from Cape Prince of Wales eastward to Franklin Bay, and also in the
interior of northern Canada south to Clinton-Colden, Aylmer, and
Artillery Lakes, where it is rather common. It has been reported
as already present by May 25 at the mouth of the Liard River, in
southwestern Mackenzie. This coincides with the time that first
arrivals are noted fully 700 miles north, at Point Barrow, Alaska.
The problem has been to ascertain the route used by these birds to
then principal nesting grounds in the interior.
For a long time it was believed that this big diver did not winter in
large numbers anywhere on the Pacific coast, and it had been supposed
that the spring route extended 2,000 miles northeastward from a
wintering ground somewhere in eastern Asia to Bering Strait, then 500
miles still northeast to round Point Barrow, then 500 miles east to
the coast of Mackenzie, and finally 700 miles south--in spring--to
the region near the eastern end of Great Slave Lake.
The yellow-billed loon is a powerful flier, and it is probable that
this suggested route is correct for those birds that breed in the
northern coastal regions. A reasonable doubt may be entertained,
however, whether the breeding birds of Great Slave Lake and
contiguous areas reach their breeding grounds by the 700-mile flight
south from the Arctic coast. Within recent years it has been found
that these birds are fairly common in the maze of channels and
islands off the coast of southeastern Alaska as late as the last of
October and in February. Possibly they are present there during the
period from November through January also, or they may at that time
move farther offshore and so escape detection. If this region is an
important wintering ground, as seems probable, then it is likely that
the breeding birds of the interior reach their nesting grounds by
a flight eastward across the mountains, a trip that is well within
their flying ability, rather than by a circuitous route around the
northern coast. The air-line distance from southeastern Alaska to the
mouth of the Liard River is in fact less than the distance to that
point from the mouth of the Mackenzie.
[Illustration: B2216M
Figure 29.--White-throated sparrow, a bird that apparently breeds
and winters each year in the same areas, but either travels by
different routes or, at least, does not make the same stops, while on
migration.]
Differing routes to various parts of a large breeding or wintering
ground, and used by large groups of individuals of other species,
are not unknown. For example, the redhead duck is one of the common
breeding ducks of the Bear River marshes of Utah, where a great many
have been banded each summer. The recovery records of banded redheads
show that while many travel westward to California, others start
their fall migration in the opposite direction and, flying eastward
across the Rocky Mountains, either turn southeast across the plains
to the Gulf of Mexico, or deliberately proceed in a northeasterly
direction to join the flocks of this species moving toward the
Atlantic coast from the prairie regions of southern Canada.
=CONCLUSIONS=
The migration of birds as it is known today had its beginning in
times so remote that its origins have been entirely obscured, and
it can be interpreted now only in terms of present conditions. The
causes underlying migration are exceedingly complex. The mystery
that formerly cloaked the periodic travels of birds, however, has
been largely dispelled through the fairly complete information that
is now available concerning the extent and times of the seasonal
journeys of most of the species. Many gaps, however, still remain
in our knowledge of the subject. Much has been learned, and present
knowledge is being placed on record, but it must be left to future
study to clear away many of the uncertainties that continue to make
bird migration one of the most fascinating subjects in the science of
ornithology.
Each kind of bird seems to have its own reaction to its environment,
so that the character of movement differs widely in the various
species, and seldom do any two present the same picture. In
fact, bird migration has been described as a phase of geographic
distribution wherein there is a more or less regular seasonal
shifting of the avian population caused by the same factors that
determine the ranges of the sedentary species. If this view is
correct, then it must be recognized that the far-reaching works of
man in altering the natural condition of the earth's surface can so
change the environment necessary for the well being of the birds as
to bring about changes in their yearly travels. The nature and extent
of the changes wrought by man on the North American Continent are
easily apparent. Forests have been extensively cut away and their
places have been taken by second growth or cultivated land, and wide
stretches of prairie and plain have been broken up, irrigated, and
devoted to agriculture. These great changes are exerting a profound
effect upon the native bird populations, and the various species may
be either benefited or adversely affected thereby.
The Federal Government, has recognized its responsibility to the
migratory birds under changing conditions brought about by man, and
by enabling acts for carrying out treaty obligations, it is now
giving many important species legal protection under regulations
administered by the Bureau of Biological Survey. Much is being done
by legislation for the welfare of the birds. The effectiveness of
these conservation laws, however, is increased in the same measure
that the people of the country become acquainted with the facts
in the life histories of the migrants and interest themselves
personally in the well being of the various species. Long before the
white man came to America the birds had established their seasonal
lanes of migration throughout the Western Hemisphere, as here
outlined. The economic, inspirational, and esthetic values of these
migratory species dictate that they be permitted to continue their
long-accustomed and still mysterious habits of migration from clime
to clime.
=BIBLIOGRAPHY=[4]
[Footnote 4: Since almost every faunal paper on birds has a bearing
on the subject of migration, only a few can be listed in this
publication. Those included were selected to aid the student wishing
to pursue the subject further and to cover not only all cited in the
text but also others consulted and used in its preparation.]
(1) Allard, H. A.
1928. BIRD MIGRATION FROM THE POINT OF VIEW OF LIGHT AND LENGTH OF
DAY CHANGES. Amer. Nat. 62: 385-408.
(2) Austin, O. L., Jr.
1928. MIGRATION-ROUTES OF THE ARCTIC TERN (STERNA PARADISAEA
BRUNNICH). Northeastern Bird Banding Assoc. Bull. 4: 121-125.
(3) Baird, S. F.
1866. THE DISTRIBUTION AND MIGRATIONS OF NORTH AMERICAN BIRDS.
Amer. Jour. Sci. (2) 41: 78-90, 184-192, 337-347.
(4) Clarke, W. E.
1912. STUDIES IN BIRD MIGRATION. 2 V., illus. London.
(5) Cooke, W. W.
1888. REPORT ON BIRD MIGRATION IN THE MISSISSIPPI VALLEY IN THE
YEARS 1884 AND 1885. U. S. Dept. Agr., Div. Econ. Ornith.
Bull. 2, 313 pp., illus.
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1904. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN WARBLERS. U. S.
Dept. Agr., Div. Biol. Survey Bull. 18, 142 pp.
(7) ------------