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.]
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
const 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 Gidf 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.