------------------------------------------------- Mackenzie Valley-Great Lakes-Mississippi Valley Route and Tributaries -------------------------------------------------
The route extending from the Mackenzie Valley past the Great Lakes and down the Mississippi Valley is easily the longest of any in the Western Hemisphere. Its northern terminus is on the Arctic coast in the regions of Kotzebue Sound, Alaska, and the mouth of the Mackenzie River, while its southern end lies in Argentina. Nighthawks, barn swallows, blackpoll warblers, and individuals of several other species that breed northward to the Yukon Territory and Alaska must cover the larger part of the route twice each year.
[Illustration: _Figure 20. Principal migratory routes of the canvasback. The major route of travel extends from breeding areas in central Canada southeast across the Great Lakes and either south down the Mississippi River or east to Chesapeake Bay (After Stewart et al 1958)._]
For more than 3,000 miles--from the mouth of the Mackenzie to the delta of the Mississippi--this route is uninterrupted by mountains. In fact, the greatest elevation above sea level is less than 2,000 feet. Because it is well timbered and watered, the entire region affords ideal conditions for its great hosts of migrating birds. It is followed by such vast numbers of ducks, geese, shorebirds, blackbirds, sparrows, warblers, and thrushes that observers stationed at favorable points in the Mississippi Valley during the height of migration can see a greater number of migrants than can be noted anywhere else in the world.
When many of these species, including ducks, geese, robins, and yellow-rumped warblers, arrive at the Gulf coast, they spread out east and west for their winter sojourn. Others, despite the perils of a trip involving a flight of several hundred miles across the Gulf of Mexico, fly straight for Central and South America. This part of the route is a broad "boulevard" extending from northwestern Florida to eastern Texas and southward across the Gulf of Mexico to Yucatan and the Isthmus of Tehuantepec (Fig. 18, route 4). This route appears to have preference over the safer but more circuitous land or island routes by way of Texas or Florida. During the height of migration some of the islands off the coast of Louisiana are wonderful observation points for the student of birds, as the feathered travelers literally swarm over them.