Figure 20.--Principal migration routes used by birds in passing from North America to winter quarters in the West Indies, Central America, and South America. Route no. 4 is the one used most extensively; only a few species make the 2,400-mile flight from Nova Scotia to South America.] 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. [Illustration: B4767M 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.] [Illustration: B4768M 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. fidva), 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.]