Easily the longest flyway of any in the Western Hemisphere is that
extending from the Mackenzie Valley past the Great Lakes and down the
Mississippi River, including its tributaries. Its northern terminus
is on the Arctic coast in the regions of Kotzebue Sound, Alaska, and
the mouth of the Mackenzie River, while its southern end lies in
Patagonia (fig. 21). During the spring migration some of the shore
birds traverse the full extent of this great path, and it seems
likely that the nighthawk, the barn swallow, the blackpoll warbler,
and individuals of several other species that breed north to Yukon
and Alaska must twice each year cover the larger part of it.
For more than 3,000 miles--from the mouth of the Mackenzie to the
Delta of the Mississippi--this flyway is uninterrupted by mountains.
In fact, there is not even a ridge of hills on the route high
enough to interfere with the movements of the feathered travelers,
and the greatest elevation above sea level is less than 2,000
feet. Well timbered and watered, the entire region affords ideal
conditions for the support of its great hosts of migrating birds.
This route is followed by such vast numbers of ducks, geese, shore
birds, blackbirds, sparrows, warblers, and thrushes, that observers
stationed at favorable points in the Mississippi Valley during
the height of migration can see a greater number of species and
individuals than can be noted anywhere else in the world.
Starting in the region of Kotzebue Sound, Alaska, the route extends
eastward across northern Alaska and joins another that has its
origin at the mouth of the Mackenzie River (fig. 21). The line of
flight then trends a little east of south through the great lake
system of central Canada, where it is joined by 2 or 3 other routes
from the northeast that have their origin on the central Arctic
coast. Continuing southward the migrating flocks are constantly
augmented by additions to their numbers as they pass over the great
breeding grounds of central and southern Canada. Upon reaching the
headwaters of the Missouri and Mississippi Rivers the route follows
these streams to the Gulf coast. Arriving in this latitude many
species, including ducks and geese, the robin, the myrtle warbler,
and some others spread out east and west for their winter sojourn.
Others, despite the perils of a trip involving a flight of several
hundred miles across the Gulf of Mexico, strike out boldly for
Central America and South America. This part of the route is a broad
"boulevard" extending from northwestern Florida to eastern Texas
and reaching southward across the Gulf of Mexico to Yucatan and the
Isthmus of Tehuantepec (fig. 20, route 4).
Many of the birds that breed east of the Allegheny Mountains parallel
the sea coast as they move southwestward in fall and, apparently
maintaining the same direction from northwestern Florida, cross the
Gulf to the coastal regions of eastern Mexico. On the other hand,
the birds that have come south directly through the Mississippi
Valley and the region west to the Rocky Mountains reach the coastal
plains of Mississippi, Louisiana, and Texas and continue directly
across the Gulf. The great majority of North American birds seeking
winter homes in the Tropics thus elect the short cut across the
Gulf of Mexico in preference to the longer although safer land or
island journey by way of Texas or Florida. During the height of the
migration some of the islands off the coasts of Louisiana and Texas
are wonderful observation places for the student of birds, as the
feathered travelers literally swarm over them.
One of the short cuts (fig. 20, route 5) that may be considered a
part of this great water artery of migration extends a few hundred
miles from the coast of Texas to the northern part of the State
of Vera Cruz. As the neighboring coast is arid and thus entirely
unsuited to the needs of birds that are frequenters of moist
woodlands, it is not surprising to find that this Gulf route is used
by such woodland species as the golden-winged warbler (_Vermivora
chrysoptera_), the worm-eating warbler (_Helmitheros vermivorus_),
and the Kentucky warbler (_Oporornis formosus_).
Formerly it was thought that most of the North American birds
that migrate to Central America made a leisurely trip along the
Florida coast, crossed to Cuba, and thence made the short flight
from the western tip of Cuba to Yucatan. A glance at the map would
suggest this as a most natural route, but as a matter of fact it is
practically deserted except for a few swallows and shore birds, or an
occasional land bird storm-driven from its accustomed course.
Present knowledge of the chief tributaries to the Mackenzie
Valley-Great Lakes-Mississippi Valley highway relates chiefly to
waterfowl. Reference already has been made to the flight of the
black ducks (p. 42) that reach the Mississippi Valley from southern
Ontario. Some individuals of this species banded at Lake Scugog,
Ontario, have been recaptured in succeeding seasons in Wisconsin
and Manitoba, but the majority have been retaken at points south
of the junction of the Ohio River with the Mississippi, definitely
indicating their route of travel from southern Ontario.
A second route that joins the main artery on its eastern side is the
one used by the blue goose (fig. 10), the migration route of which
is probably more nearly due north and south than that of any other
North American bird. The breeding grounds, which only recently have
been discovered, are in the Fox Basin region of Baffin Island and
on Southampton Island. In fall these geese work southward, chiefly
along the eastern shore of Hudson Bay, and upon reaching the southern
extremity of James Bay they take off for what is practically a
nonstop flight to the great coastal marshes of Louisiana west of
the delta of the Mississippi River (fig. 21). In some seasons the
flocks make intermediate stops among the islands and sand bars of the
Mississippi, as they are occasionally common in the general vicinity
of Memphis, Tenn. Most of the birds push on, however, and during
the period from the first of November to the last of March fully
90 percent of the species are concentrated in the area between the
Sabine and the Mississippi Rivers. On the return trip northward there
is sometimes a tendency for some of the blue geese to veer off toward
the Northwest, as they are occasionally abundant in eastern South
Dakota and southeastern Manitoba. It is of particular interest to
note that while some other geese and many ducks start their northward
journey at the first sign of awakening spring, the blue goose remains
in its winter quarters until the season there is far advanced,
seemingly aware that its own breeding grounds in the Arctic are still
in the grip of winter.
As shown by the route map (fig. 21) a great western highway also has
its origin in the Mackenzie River delta area and in Alaska. This is
used chiefly by the pintail and the baldpate (Mareca americana),
which fly southward through eastern Alberta to western Montana. Some
localities in this area, as for example, the National Bison Range, at
Moiese, Mont., normally furnish food in such abundance as to induce
these birds to pause in their migratory movement. Upon resuming
travel, some flocks move almost directly west across Idaho to the
valley of the Columbia River, from which they turn abruptly south to
the interior valleys of California. Others leave the Montana feeding
and resting areas and turn southeastward across Wyoming and Nebraska
to join the flocks that either are moving southward through the Great
Plains, or are to continue across Arkansas to the main Mississippi
Valley fly way.
Many redheads that breed in the Bear River marshes in Utah, take a
westerly route across Nevada to California, but some leave these
breeding grounds and fly northeastward across North Dakota and
Minnesota to join the flocks of these ducks that come out of the
prairie regions of Canada, and travel southeastward to the Atlantic
coast. This route can be well traced by the records of ducks banded
in summer in the Bear River marshes and retaken the following fall
at points in eastern Montana, Wyoming, South Dakota, North Dakota,
Minnesota, Wisconsin, Michigan, and Maryland.
Another route from these great marshes crosses the mountains in an
easterly direction, but almost immediately turns southward through
Colorado and New Mexico, and continues to winter quarters in the
Valley of Mexico (fig. 21 and fig. 20, route 6). This route also
represents the travels of many of the land birds of the Rocky
Mountain region. Such birds perform comparatively short migrations,
most of them being content to stop when they reach the middle
districts of Mexico, only a few passing east beyond the southern part
of that country.
This account of the Mackenzie Valley-Great Lakes-Mississippi Valley
route shows the great importance of this highway and also its
complicated nature. It receives accretions from both the northeast
and the northwest, while branch routes make wide detours toward the
Pacific coast before turning back to the parent fly way. This flyway
is notable for its great length, as it extends from the Arctic-coast
to Patagonia; and for its width east and west, as in North America it
reaches from the Allegheny Mountains westward to the Great Basin.