Birds tend to use regular corridors for migration flights. The four main corridors or flyways in North America are the Atlantic Flyway, Mississippi Flyway, Central Flyway, and Pacific Flyway. There are numerous minor flyways scattered between the main corridors. Migration can occur 365 days a year and seasons overlap. Some birds fly as low as 2000 feet, others have been recorded at 29,000 feet! Some fly nonstop while others can take up to four months.
Diurnal migrants are generally hawks, shorebirds, ducks, and geese, all taking advantage of thermals and/or favorable wind patterns during the day. Swifts and swallows feed on insects while migrating. Nocturnal migrants are generally songbirds who take advantage of cooler temperatures, less wind, and fewer predators.
August 2014: Birds recorded moving south: green and blue-winged teal, northern shovelers, sandpiper species, white-crowned sparrows, common nighthawks, summer tanagers, and orioles. Warblers include orange-crowned, Nashville, Wilson’s, and Townsend’s. Swainson’s hawks, broad-winged hawks, bald eagles, American kestrels, and ospreys (one banded osprey with a transmitter flew from Montana to Veracruz, Mexico, in 10 days – see www.raptorview.org).
September 2014: Swainson’s hawks, sharp-shinned hawks, bald eagles, American kestrels, Franklin’s and ring-billed gulls, ruby-crowned kinglets, more warblers, and sparrows including white-crowned, Brewer’s, and Savannah.
October along the Atlantic flyway typically includes golden eagles, red-tailed hawks, Cooper’s hawks, red-shouldered hawks, peregrine falcons, and turkey and black vultures.
For 15 fun facts about bird migration and more: http://birding.about.com/od/birdbehavior/a/15-Fun-Facts-About-Bird-Migration.htm
For more facts regarding preparation for migration, timing, altitudes, and navigation: http://www.zoosociety.org/conservation/bwb-asf/library/BirdMigrationFacts.php
For Atlantic flyway weekly counts, http://www.hawkmountain.org/science/hawk-mountain-raptorcount/hawk-count~default.aspx?id=518
In Arizona at the Grand Canyon, http://www.hawkwatch.org/our-work/annual-monitoring/fall-migration/item/75-grand-canyon-raptor-migration-project
For regional forecasts of what is moving through the different flyways: www.birdcast.info/forecast