ATLANTIC OCEANIC ROUTE
By reference to [figure 20] it will be noted that route no. 1 is almost entirely oceanic, passing directly over the Atlantic Ocean from Labrador and Nova Scotia to the Lesser Antilles, and then through this group of small islands to the mainland of South America. It is not used by any of the smaller land birds, but is followed chiefly by thousands of water birds and by shore birds of several species, the adult golden plover being a notable example. Since it lies entirely over the sea, this route is definitely known only at its terminals and from occasional observations made on Bermuda and other islands in its course. Some of the shore birds that breed on the Arctic tundras of Mackenzie and in Alaska fly southeastward across Canada to the Atlantic coast and finally follow the oceanic route to the mainland of South America. The golden plover may accomplish the whole 2,400 miles without pause or rest, in fair weather the flocks passing Bermuda and sometimes even the islands of the Antilles without stopping. Although most birds make their migratory flights either by day or by night, the golden plover in this remarkable journey flies both day and night. As it swims lightly and easily it may make a few short stops along the way, and it has been actually seen resting on the ocean. Other shore birds have been observed busily feeding in that great area of ocean known as the Sargasso Sea, where thousands of square miles of floating seaweed teem with marine life.
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Figure 21.—Migration routes of North American birds. Though this map was prepared chiefly to show the flyways used by waterfowl, most of these routes also are utilized by innumerable land birds. For example, the important Mackenzie Valley-Great Lakes-Mississippi Valley route is shown (with its tributaries) from the Arctic coast to the delta of the Mississippi River.
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Figure 22.—Distribution and migration of the golden plover, Pluvialis dominica. Adults of the eastern form (P. d. dominica) migrate across northeastern Canada and then by a nonstop flight reach South America. In spring they return by way of the Mississippi Valley. Their entire route is therefore in the form of a great ellipse with a major axis of 8,000 miles and a minor axis of about 2,000 miles. The Pacific golden plovers (P. d. fulva), which breed in Alaska, apparently make a nonstop flight across the ocean to Hawaii, the Marquesas Islands, and the Low Archipelago, returning in spring over the same route.
The annual flight of the adult golden plover is so wonderful that it may be given in some detail, particularly since it is one of the exceptions to the general rule that spring and fall movements are over the same routes ([fig. 22]). After reaching the South American coast the birds make a short stop and then continue overland to the pampas of Argentina, where they remain from September to March. Leaving their winter quarters, they cross northwestern South America and the Gulf of Mexico, reaching the North American mainland on the coasts of Texas and Louisiana. Thence they proceed slowly up the Mississippi Valley, and by the early part of June are again on their breeding grounds, having performed a round-trip journey in the form of an enormous ellipse with the minor axis about 2,000 miles and the major axis 8,000 miles, reaching from the Arctic tundras to the pampas of Argentina. The older birds are probably accompanied by some of the young, perhaps those from early nestings, but most of the immatures leave their natal grounds late in summer and move southward through the interior of the country, re turning in spring over essentially the same course. The elliptical route is therefore used chiefly by fully adult birds.