Breeding range.—Until about 1935 Swainson’s warbler was considered to be confined in summer to the southern canebrakes and coastal marshes. It is now known to breed north to extreme southern Illinois, probably (seen in breeding season to Olive Branch, Duquoin, and Mount Carmel); southeastern Kentucky (Big Black Mountain); central to northern West Virginia (Charleston, Mount Lookout, Sutton, and Buzzard Rocks, Monongalia County); and southeastern Maryland (Pocomoke River Swamp). East to eastern Maryland (Pocomoke River Swamp); eastern Virginia (Warwick County and Dismal Swamp); eastern North Carolina (New Bern, Lake Ellis, and Red Springs); eastern South Carolina (Summerton, Charleston, and Yemassee); eastern Georgia (Savannah and Okefinokee Swamp); and northeastern Florida (Jacksonville). South to northern Florida (Jacksonville, Oldtown, Whitfield, and Pensacola) and southern Louisiana (Mandeville, New Orleans, and Baton Rouge). West to eastern Louisiana (Baton Rouge, Bayou Sara, and Jena); central Arkansas (Camden and Conway); extreme northeastern Oklahoma (Copan); and central Missouri (Concordia).
Within this large breeding area are two almost discontinuous breeding ranges: the coastal and swamp range long considered the only home of the species; and the more recently discovered mountain home along the slopes of the Allegheny Mountains from northern West Virginia nearly to the Georgia line where it has been found to an altitude of nearly 3,000 feet.
Winter range.—The winter home of the Swainson’s warbler is very imperfectly known from a dozen or more specimens, most of which are from Jamaica where it has been listed as a rare winter resident. There are records also from the Swan Islands (March 1); Santa Lucia, Quintana Roo; Pacaytain, Campeche; and the city of Veracruz. Two specimens have been taken near Habana, Cuba; one on September 25, the other in April; and one near Guantánamo on January 18, 1914.
Migration.—Dates of spring departure are: Jamaica, April 8. Cuba—Habana, April 14.
Early dates of spring arrival are: Florida—St. Petersburg, March 25. Alabama—Autaugaville, April 3. Georgia—Savannah, March 25. South Carolina, April 1. Louisiana—New Orleans, March 30. Mississippi—Biloxi, March 31. Tennessee—Memphis, April 20. Texas—Point Bolivar, April 17.
Late dates of fall departure are: Texas—Kemah, September 27. Tennessee—Sulphur Springs, September 9. Mississippi—Gulfport, October 6. South Carolina—Charleston, October 10. Georgia—Savannah, October 18. Alabama—Greensboro, September 6. Florida—Pensacola, October 2; Sombrero Key (4 struck lighthouse November 10).
Dates of fall arrival are: Tamaulipas—Matamoros, August 29. Jamaica, October 1.
Casual records.—A specimen was recorded near Corsicana, Tex., on August 24, 1880; another was collected at Kearney, Nebr., on April 9, 1905; and one near Holly, Prowers County, Colo., on May 12, 1913.
Egg dates.—Florida: 3 records, May 7. Georgia: 35 records, May 4 to July 13; 19 records, May 29 to June 17, indicating the height of the season. South Carolina: 28 records, May 2 to June 30; 14 records. May 12 to June 12 (Harris).