ATLANTIC COAST ROUTE AND TRIBUTARIES
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 Rico, 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.
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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 flyways 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.