Typically birds use this route because no mountains or ridges of hills block the path over its entire extent.[2] Good sources of water, food, and cover exist over its entire length. About 40% of all North American migrating waterfowl and shorebirds use this route.[3]
The other primary migration routes for North American birds include the Atlantic, Central and Pacific Flyways. The Central Flyway merges with the Mississippi Flyway between Missouri and the Gulf of Mexico. In the northern portions of the Upper Mississippi River, the birds congregate in the Driftless Area.[4]