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. 17], 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 draw-back 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. Nevertheless, many thousands of coots, widgeons, pintails, blue-winged teal, and other waterfowl and shorebirds regularly spend the winter season in the coastal marshes and the inland lakes and ponds of Cuba, Hispaniola, and Puerto Rico.
The map ([fig. 17]) also will show that route No. 3 presents a direct line of travel for Atlantic coast migrants en route to South America, although it involves much longer flights. It is used almost entirely by land birds. After taking off from the coast of Florida there are only two intermediate land masses where the migrants may 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 this number elect to remain for the winter months. The others do not hesitate to fly the 90 miles between Cuba and Jamaica, but from that point to the South American coast there is a stretch of islandless ocean fully 500 miles across. Scarcely a third of the North American migrants leave the forested mountains of Jamaica to risk the perils of this ocean trip. Chief among these is the bobolink, which so far outnumbers all other birds using this route that it may be well called the "bobolink route" ([fig. 19]). As traveling companions along this route, the bobolink may meet a vireo, a kingbird, and a nighthawk from Florida; the chuck-wills-widow of the Southeastern States; the black-billed and the yellow-billed cuckoos from New England; the gray-cheeked thrush from Quebec; bank swallows from Labrador; and the blackpolled warbler 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.
Figure 19.—Distribution and migration of the bobolink. In crossing to South America most of the bobolinks use route 3 ([fig. 17]), showing no hesitation in making the flight from Jamaica across an islandless stretch of ocean. It will be noted that colonies of these birds have established themselves in western areas, but in migration they adhere to the ancestral flyways and show no tendency to take the short cut across Arizona, New Mexico, and Texas. ([See p. 55.])
Formerly it was thought that most of the North American land 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 shorebirds, or an occasional land bird storm-driven from its accustomed course. What actually happens is that in the fall many of the birds that breed east of the Allegheny Mountains travel parallel to the seacoast in a more or less southwesterly direction and, apparently maintaining this same general course from northwestern Florida, cross the Gulf of Mexico to the coastal regions of eastern Mexico.
The routes used by the Atlantic brant merit some detail for the reason that these were long misunderstood. These birds winter on the Atlantic coast, chiefly at Barnegat Bay, N. J., but (depending upon the severity of the season and the food available) south also to North Carolina. Their breeding grounds are in the Canadian arctic archipelago and on the coasts of Greenland. According to the careful studies of Lewis (1937), the main body travels northward in spring along the coast to the Bay of Fundy, hence overland to Northumberland Strait, which separates Prince Edward Island from the mainland of New Brunswick and Nova Scotia. A minor route appears to lead northward from Long Island Sound by way of such valleys as those of the Housatonic and Connecticut Rivers, and on across southern Quebec to the St. Lawrence River.
After spending the entire month of May feeding and resting in various parts of the Gulf of St. Lawrence, the eastern segment of the brant population suddenly resumes its journey by crossing to the north shore of the St. Lawrence estuary. The Bay of Seven Islands, in this general region, is the point of departure for long overland flights that are made by the two segments of the population. The eastern and larger of these appears to fly almost due north to Ungava Bay and from there to nesting grounds, probably in Baffin Island and Greenland. The smaller segment travels a route that is but slightly north of west to the southeastern shores of James Bay, although somewhere to the east of that area some of the flocks take a more northwesterly course, descending the Fort George River to reach the eastern shore of James Bay about two-thirds of the distance north of its southern extremity. Upon their arrival at either of these two points on James Bay, the brant of this western segment turn northward and proceed through the eastern part of Hudson Bay to their breeding grounds, probably in western Baffin Island, Southampton Island, and other islands in the Canadian Arctic.
In general, the fall migration of the brant follows the routes utilized in the spring. At this season, when gathering for the flight of 570 miles to the St. Lawrence River, they appear only on the western and southern shores of Ungava Bay. Also, it appears that most of the birds of the western segment, instead of following the eastern shores of Hudson and James Bays, turn southwestward across the former, by way of the Belcher Islands, to Cape Henrietta Maria and from there south along the western shores of James Bay by way of Akimiski and Charlton Islands. At the southern end of James Bay they are joined by those that have taken the more direct route along the east coasts of the bays and all then fly overland 570 miles to the estuary of the St. Lawrence River.
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, redheads, scaup ducks, 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, 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 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 the St. Clair Flats, between Michigan and Ontario, swing abruptly to the 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 at Lake Scugog, Ontario.
The white-winged scoter, which also breeds in the interior of the continent from northern North Dakota north to the Arctic coast, was at one time credited with an elliptical migration route, at least insofar as those wintering on the Atlantic coast are concerned. This sea duck nests only near fresh water but spends the winters on the ocean along both the Atlantic and Pacific coasts of the United States. It migrates over land surfaces mainly at night and it is now believed that after working northward to the waters of Long Island Sound it starts up the valleys of the Hudson and Connecticut Rivers and flies overland to the Great Lakes, from which region it continues west and northwest to the breeding grounds, returning to its winter quarters over the same route. Early ideas alleging an elliptical route probably arose from the fact that great numbers of first-year nonbreeding birds regularly pass up the New England coast, cross the Gulf of St. Lawrence and spend the summer loafing off the coast of Labrador. In the fall these birds form into large flocks and retrace their flight, chiefly during daylight hours, to winter quarters from southeastern Maine south at least to Chesapeake Bay. As it was not known that the white-winged scoter does not usually breed until it is 2 years old, and since the southward movement of yearling birds was conspicuous while the travels of those from the nesting grounds were chiefly at night, the theory was advanced that the latter flew 1,500 miles due east from the region west of Hudson Bay to the coast of Labrador, thence southward to the known winter quarters.
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 shore of Hudson Bay. From this region they move south in autumn to the point of Lower Ontario between Lakes Erie and Huron. Occasionally one of these geese will be 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 the Canada goose is abundant in migration on the coast of New England, the birds taken there rarely include any of those banded in southern Ontario. The northeastern population of these geese comes from breeding areas in New England, the Maritime Provinces of Canada, Newfoundland, and the desolate coast of Labrador, their migration being entirely coastwise. Still another cross-country route between the Mississippi Valley and the Atlantic coast remains to be briefly described. It is not yet well understood, but the banding of ducks such as the blue-winged teal on the coastal saw-grass marshes of South Carolina has revealed that there is a migration route across the Appalachians to the Mississippi Valley. Birds marked in these marshes have been retaken in Tennessee and Kentucky, as well as in other States farther north in the Mississippi Flyway.