By early October, most of the Blackburnian warblers have passed beyond the United States, en route to their winter home in South America. Professor Cooke (1904) says: “By the middle of October the earliest migrants have reached Venezuela and Ecuador. The main army of the Blackburnians pass the south end of the Alleghenies between September 25 and October 5, and during the first two weeks of October are moving through San José, Costa Rica, and by early in November are settled for the winter in Perú.”
Dickey and van Rossem (1838) refer to it as a “fairly common fall migrant and very rare winter visitant in the Arid Lower Tropical Zone” in El Salvador, but “not seen in spring.”
Winter.—Dr. Alexander F. Skutch contributes the following notes: "Rarely recorded, and apparently only as a bird of passage, in Guatemala, the Blackburnian warbler is a moderately abundant winter resident in Costa Rica. Here it passes the winter months on both slopes of the Cordillera, from about 1,500 to 6,000 feet above sea-level, but is far more abundant above than below 3,000 feet. It is found in midwinter both in heavy forest and among scattered tall trees. Although the birds appear to arrive in flocks in late August or September, they soon disperse through the woodland and show slight sociability. Yet one or two may at times join a mixed flock of Tennessee warblers and other small birds. Restlessly active, the Blackburnian warbler forages well above the ground, where it is difficult to see. I have never heard its song in Central America.
“Early dates of fall arrival are: Guatemala—Chimoxan (Griscom), October 1; Panajachel (Griscom), October 4. Costa Rica—San José (Cherrie), September 8; San José (Underwood), Septem 10; La Hondura (Carriker), September 19; San Isidro de Coronado, September 8, 1935; Vara Blanca, August 19, 1937; Cartago, September 13, 1938; Murcia, September 14, 1941; Basin of El General, September 16, 1936; Ujarrás (Carriker), September 12. Ecuador—Volcán Tungurahua, 7,400 feet, October 12, 1939.
“Late dates of spring departure from Central America are: Costa Rica—Basin of El General, March 25, 1936, March 13, 1937 and April 18, 1943; Vara Blanca, May 7, 1938; Pejivalle, April 23, 1941; Bonilla (Basulto), April 10. Guatemala—Finca Sepacuite (Griscom), May 10.”
DISTRIBUTION
Range.—Southern Canada east of the Great Plains to Central Perú.
Breeding range.—The Blackburnian warbler breeds north to southern Manitoba (Lake St. Martin and Berens Island, Lake Winnipeg); central Ontario (Lac Seul, Lake Abitibi, and North Bay; has occurred at Trout Lake); and central Quebec (Blue Sea Lake, Lake Albanel, rarely; Lake St. John and Gaspé; possibly Pointe de Monts and Natashquan). East to eastern Quebec (Gaspé); eastern New Brunswick (Bathurst and Tabusintac); and eastern Nova Scotia (Antigonish and Halifax). South to Nova Scotia (Halifax); southern Maine (Calais, Lewiston, and Portland); Massachusetts (Cambridge, Springfield, and Sheffield); northern New Jersey (Kittatinny Mountains); central Pennsylvania (Mauch Chunk and Carlisle); and south through the mountains of Maryland, Virginia, West Virginia, North and South Carolina and Tennessee to northern Georgia (Brasstown Bald and Burnt Mountain); western Pennsylvania (Leasureville and Meadville); northeastern Ohio (Pymatuning Swamp and possibly Geneva); northern Michigan (Bay City and Wequetonsing); northern Wisconsin (New London, Unity and Ladysmith); and northern Minnesota (Elk River, Onamia, and Itasca Park). West to northwestern Minnesota (Itasca Park) and southeastern Manitoba (Winnipeg and Lake St. Martin).
A possible future extension of range westward is seen in records from Saskatchewan: it was recorded four times near Indian Head 1888-1901; one at Last Mountain Lake in 1920, at Lake Johnston in 1922; and at Emma Lake in the summer of 1939, possibly breeding.
Winter range.—The Blackburnian warbler is reported to winter commonly in Costa Rica, but as yet has been found in Panamá only as a migrant. In South America it is found north to northern Colombia (Santa Marta region); and central northern Venezuela (Rancho Grande). East to northwestern Venezuela (Rancho Grande, Mérida, and Páramo de Tamá); the eastern slope of the Andes in Colombia (Pamplona, Bogotá, and San Antonio); Ecuador (Mount Sumaca, Machay, and Zamora); and Perú (Chinchao and Huambo). South to central Perú (Huambo and Anquimarca). West to western Perú (Anquimarca and Tambillo); Ecuador (Ambato, Quito, and Parambo); and Colombia (Concordia, Medellín, and the Santa Marta region). It is casual in migration in the Bahamas and Cuba.