The Atlantic coast is a regular avenue of travel, and along it are
many famous points for observing both land and water birds. About 50
different kinds of land birds that breed in New England follow the
coast southward to Florida and travel thence by island and mainland
to South America (fig. 20, route 2). As will be seen from the map, a
seemingly natural and convenient highway extends through the Bahamas,
Cuba, Hispaniola, Puerto Kico, and the Lesser Antilles to the South
American coast. Resting places are afforded at convenient intervals,
and at no time need the aerial travelers be out of sight of land. It
is not, however, the favored highway, and only about 25 species of
birds go beyond Cuba to Puerto Rico along this route to their winter
quarters, while only 6 species are known to reach South America by
way of the Lesser Antilles. The obvious drawback is lack of adequate
food. The total area of all the West Indies east of Puerto Rico is
less than that of Rhode Island, so that if only a small part of
the birds of the eastern United States were to travel this way, it
is doubtful whether even the luxuriant flora and fauna of tropical
habitats would provide food sufficient for their needs.
In the northern part of the Atlantic coast route is a tributary route
used by the brant (_Branta bernicla_) that is of special interest.
The southward movement of these birds is chiefly along the western
shores of Hudson Bay and thence southeastward to the Atlantic coast.
Returning in spring, they follow the coast line north to the Gulf
of St. Lawrence and then fly almost due north to their breeding
grounds on the west coast of Greenland and the islands of the Arctic
archipelago. The round trip is therefore in the form of a great
ellipse, probably 3,000 miles long by 1,000 miles wide.
The Atlantic flyway receives accretions of waterfowl from three or
four interior migration paths, one of which is of first importance,
as it includes great flocks of canvasbacks (_Nyroca valisineria_),
redheads (_N. americana_), scaup ducks (_N. marila_ and _N.
affinis_), Canada geese, and many of the black ducks that winter
in the waters and marshes of the coastal region south of Delaware
Bay. The canvasbacks, redheads, and scaups come from their breeding
grounds on the great northern plains of central Canada, follow the
general southeasterly trend of the Great Lakes (fig. 21), cross
Pennsylvania over the mountains, and reach the Atlantic coast in the
vicinity of Delaware and Chesapeake Bays. Black ducks, mallards,
and blue-winged teals (_Querquedula discors_) that have gathered
in southern Ontario during the fall leave these feeding grounds
and proceed southwest over a course that is apparently headed for
the Mississippi Valley. Many do continue this route down the Ohio
Valley, but others, upon reaching the vicinity of Lake St. Clair,
between Michigan and Ontario, swing abruptly southeast and, crossing
the mountains in a single flight, reach the Atlantic coast south
of New Jersey. This route, with its Mississippi Valley branch, has
been fully demonstrated by the recovery records of ducks banded by a
cooperator of the Biological Survey at Lake Scugog, Ontario.
The white-winged scoter (_Melanitta deglandi_), which also breeds in
the interior country from northern North Dakota north to the Arctic
coast, is another bird having an elliptical migration route, so far
as those wintering on the Atlantic coast are concerned. This duck
breeds only near fresh water and winters entirely on the ocean along
both the Atlantic and Pacific coasts of the United States. Those
wintering on the Atlantic side leave their breeding grounds west of
Hudson Bay and fly 1,500 miles almost due east to the most eastern
part of Labrador, whence they proceed southward across the Gulf of
St. Lawrence to their winter home, which extends from southwestern
Maine to Chesapeake Bay. The spring flight is made by an interior
route that traverses the valleys of the Connecticut, Hudson, and
Ottawa Rivers, and thence passes west and north to the breeding
grounds.
A study of the Canada geese that winter abundantly in the waters of
Back Bay, Va., and Currituck Sound, N. C., reveals another important
tributary to the Atlantic coast route. Banding has shown that the
principal breeding grounds of these birds are among the islands and
on the eastern shores of Hudson Bay (fig. 21). From this region they
move south in fall to the point of lower Ontario between Lakes Erie
and Huron. Some of the banded geese are recovered in the Mississippi
Valley, but the great majority are retaken either on their breeding
grounds or on the Atlantic coast south of Delaware Bay, showing
another instance of a long cross-country flight by waterfowl.
Although Canada geese are abundant in migration on the coast of New
England, the birds taken there do not include any that were banded
in southern Ontario. Again, banding has shown that the New England
visitants come from other breeding areas, chiefly Newfoundland and
the desolate coast of Labrador, and that their migration is entirely
coastwise.
Still another cross-country route between the Mississippi Valley
and the Atlantic coast may be briefly described. While not yet
well understood, a hitherto unsuspected migration route across the
Alleghenies to the Mississippi Valley has been revealed by the
banding of blue-winged teal, on the coastal sawgrass marshes of
South Carolina. Birds marked in these marshes have been retaken in
Tennessee and Kentucky as well as in States farther north in the
Mississippi Valley. Several species of shoal-water ducks, including
this dainty little teal and the shoveler (_Spatula clypeata_), are
more or less common winter residents in the South Carolina marshes,
but are less common or even decidedly rare in most of the coastal
marshes farther north, so this cross-country route connecting two
main arteries of migration seems to be of considerable importance.
[Illustration: B4762M
Figure 23.--Distribution and migration of the bobolink. In crossing
to South America most of the bobolinks use route no. 3 (fig. 20),
directly from Jamaica across an unbroken stretch of ocean. Colonies
of these birds have established themselves in several areas in the
western United States, but in migration they adhere to the ancestral
fiyways and show no tendency to take the short cut across Arizona,
New Mexico, and Texas.]
Referring again to figure 20, it is noted that route no. 3 presents
a much more direct line of flight for the Atlantic coast migrants
to South America than the others, although it involves much longer
flights. It is used almost entirely by land birds. After taking off
from the coast of Florida the migrants find only two land masses on
the way where they can pause for rest and food. Nevertheless, tens
of thousands of birds of some 60 species cross the 150 miles from
Florida to Cuba, where about half of them elect to remain for the
winter. The others fly the 90 miles between Cuba and Jamaica. From
that point to the South American coast, however, there is a stretch
of unbroken ocean fully 500 miles across, and scarcely a third of
the North American migrants leave the forested mountains of Jamaica
to risk the perils of this ocean trip. Chief among those that do is
the bobolink (_Dolichonyx oryzivorus_), which so far outnumbers all
other birds using this fly way that route no. 3 may well be called
"the bobolink route" (fig. 23). As traveling companions along this
route the bobolinks may meet vireos, kingbirds, and nighthawks
from Florida; the chuck-will's-widow (_Antrostomus carolinensis_)
of the Southeastern States; black-billed and yellow-billed cuckoos
(_Coccyzus erythropthalmus_ and _C. americanus_) from New England;
gray-cheeked thrushes from Quebec, bank swallows (_Riparia riparia_)
from Labrador; and blackpoll warblers from Alaska. Sometimes this
scattered assemblage will be joined by a tanager or a wood thrush
but "the bobolink route" is not popular with the greater number of
migrants, and although many individuals traverse it, they are only a
small fraction of the multitudes of North American birds that spend
the winter in South America.