All through the mountainous districts, both in the interior and coastwise, the black-throated green warbler is an extremely common winter visitant; in fact, it constitutes, at levels between 3,500 and 5,000 feet, fully 90 per cent of the nonresident warbler population. The numerous flocks of from a dozen to half a hundred individuals invariably formed the nuclei about which gathered smaller numbers of other insectivorous species resident and nonresident. The black-throated green warbler showed decided preference for the oak and pine association at the altitudes mentioned, although it was by no means confined to such environments.
Many were seen in the coffee cover down to 3,000 feet on Mt. Cacaguatique and 2,300 feet at San Salvador. A few birds reach as high as 8,000 feet, at which level they were found in both pines and cloud forest on Los Esesmiles. * * * The average winter range of virens lies approximately 3,000 feet below that of townsendi, although strays and vagrants make the extremes of altitude nearly the same in both cases.
DISTRIBUTION
Range.—Eastern North America from southern Canada to Panamá.
Breeding range.—The black-throated green warbler breeds north to central western and northeastern Alberta (Grande Prairie, Peace River and Chipewyan); central Saskatchewan (Big River and Emma Lake); southern Manitoba (Brandon and Hillside Beach); southern Ontario (Lac Seul, Rossport, Chapleau, and Lake Abitibi; casual or accidental at Moose Factory); central Quebec (Mistassini Post, Upper St. Maurice River, Godbout, Mingan, and Natashquan); and casually in southeastern Labrador (Battle Harbor). East to southeastern Quebec (Natashquan); southwestern Newfoundland (Spruce Brook and Tompkins); Nova Scotia (Sydney, Halifax, and Barrington); the coast of New England; Long Island (Miller’s Place); northern New Jersey (Demarest and Dover); central Pennsylvania (Pottsville and Carlisle); central Maryland (Thurmont); central and southeastern Virginia (Charlottesville and Dismal Swamp); North Carolina (Lake Mattamuskeet); and central South Carolina (Charleston). South to South Carolina (Charleston); northern Georgia (Pinelog Mountains and Lookout Mountain); northeastern Alabama (Sand Mountain); southeastern Kentucky (Big Black Mountain and Jackson); central Michigan (Bay City and Mason County); northern Wisconsin (New London and Ladysmith); central Minnesota (Lake Minnetonka, Mille Lacs, and Cass Lake); southwestern Manitoba (Aweme); and southern Alberta (Brooks). West to western Alberta (Brooks, Glenevis, Sturgeon Lake, and Grande Prairie).
Winter range.—The black-throated green warbler is found in winter north to southern Texas (Arroya Colorado, Willacy County); and Yucatán (Tunkas and Chichén-Itzá). East to Yucatán (Chichén-Itzá); the coast of Quintana Roo; northeastern El Salvador (Mount Cacaguatique); eastern Costa Rica (Volcán Irazú); and central Panamá (Veragua); casual or accidental to northern Colombia (one record; Cincinnati, Santa Marta region). South to Panamá (Veragua and Volcán de Chiriquí). West to western Panamá (Volcán de Chiriquí); western Costa Rica (El General); western El Salvador (San Salvador); western Guatemala (Volcán de Agua and Dueñas); Oaxaca (Tehuantepec); western Morelos (Curnavaca); Puebla (Metlatoyuca); southern Tamaulipas (Altamira); probably eastern Nuevo León (Linares); and southern Texas (Santa Maria and Arroya Colorado).
The black-throated green warbler has apparently extended its winter range northward in recent years. Except for a single specimen taken at Brownsville in January 1911, it was not known to winter in Texas until 1933-34, when about 30 birds were seen. Since then it has increased and spread over most of Cameron County and to the southern border of Willacy County. One was recorded on Bull’s Island, S. C., on January 8 and 9, 1940.
The species is also rare or casual in winter or migration in the West Indies: Cuba (Habana and Isle of Pines); Jamaica; Haiti (Île à Vache); Puerto Rico (Adjuntas); and the islands of St. Croix, Guadeloupe, and Dominica; also Watling Island, Bahamas.
The ranges as outlined apply to the entire species of which two geographic races are recognized. The northern black-throated green warbler (D. v. virens) is found in all the breeding range except the coastal region, from southeastern Virginia to South Carolina, which is occupied by Wayne’s black-throated green warbler (D. v. waynei).