Field marks.—The male black-throated blue warbler could hardly be mistaken for anything else; there is no other American warbler that is at all like it. The blue back, the extensive black throat, the white patch near the bases of the primaries, the white under parts, and the white spots on the inner webs of the three outer tail feathers are all diagnostic. Fortunately, the fall plumage is essentially the same. But the female is one of the most difficult of the warblers to recognize, olive-green above and buffy below; the only distinctive marks are the white patches in the wings and tail, similar to those of the male, but smaller, duller, and sometimes obscure.
Fall.—As soon as the molting season is over, late in August, old and young birds begin to drift away from their summer haunts; most of them depart from New England during September or even late August. Birds from New England and farther north pass through the Atlantic Coast States to Florida and the West Indies, while those from the interior migrate slightly southeastward and across the lower Alleghenies to join them. Professor Cooke (1904) writes:
Black-throated blue warblers strike the lighthouse at Sombrero Key in greater numbers than any other kind of bird, particularly during the fall migration. * * * In five years’ time they struck the light on seventy-seven nights, and as a result 450 dead birds were picked up on the platform under the lantern. Probably a still larger number fell into the sea. Adding to these those that were merely stunned and that remained on the balcony under the light until able to resume their journey, the keeper counted 2,000 birds that struck. There were two nights, however, when the numbers of this species were so great that no attempt was made to count them. The Fowey Rocks lighthouse was struck on thirty different nights. It is certain, therefore, that the black-throated blue warbler passes in enormous numbers along both coasts of southern Florida.
Winter.—Professor Cooke (1904) observes that “the winter home of the black-throated blue warbler is better defined than that of any other common warbler, and allows a very exact determination of the square miles of territory occupied by it at this season. Cuba, Haiti, and Jamaica, with a combined area of 74,000 square miles, are doubtless occupied during the winter by the great majority of the individuals of the species. The remaining birds do not probably cover enough territory to bring the total to 80,000 square miles. This is a small area compared with that occupied during the breeding season.” In his Birds of Cuba, Dr. Thomas Barbour (1923) writes:
The Black-throated Blue Warbler is excessively common, early to arrive and late to leave. It is one of the tamest and most confiding species, and one to be found in all sorts of situations. Early pleasant days in Cuba spent at Edwin Atkins’ plantation, Soledad, near Cienfuegos, brought a great surprise, for I found it not uncommon to have these little Warblers enter my room through the great ever open windows and flit from couch to chair. This happened often, notably at Guabairo, not far from Soledad. So inquisitive and confiding are they, that one can hardly recognize the rather retiring dweller in woodland solitude which we know in the North.
DISTRIBUTION
Range.—Eastern North America, from southern Canada to northern South America.
Breeding range.—The black-throated blue warbler breeds north to southwestern and central Ontario (Lac Seul, Kapuskasing, and Lake Timiskaming); and southern Quebec (Blue Sea Lake, Quebec, Godbout, and Mingan). East to southern Quebec (Mingan, Grand Grève, and the Magdalen Islands); eastern Nova Scotia (Cape Breton Island and Halifax); southern Maine (Ellsworth and Auburn); southeastern Massachusetts (Taunton); Connecticut (Hadlyme); northeastern Pennsylvania (Lords Valley and Pocono Mountain); and southward through the Alleghanies to Northwestern South Carolina (Mountain Rest); northeastern Georgia (Rabun Bald, Brasstown Bald, and Young Harris). South to northern Georgia (Young Harris); southeastern Tennessee (Beersheba Springs); southeastern Kentucky (Log Mountain and Black Mountain); northeastern Ohio (Wayne Township and Pymatuning Bog); northern Michigan (Douglas Lake and Wequetonsing); northern Wisconsin (Fish Creek, Mamie Lake, and Perkinstown); and northern Minnesota (Kingsdale, Cass Lake, and White Earth; possibly sometimes near Minneapolis). West to northern Minnesota (White Earth) and western Ontario (Lac Seul). The species very probably breeds rarely in Manitoba or Saskatchewan where there are as yet only a few records and it is a recent arrival. At Emma Lake, Saskatchewan, 40 miles north of Prince Albert, 5 were observed June 27 to July 2, 1939. The first record for the Province was a specimen collected on October 21, 1936, at Percival, 100 miles east of Regina. It is a rare but tolerably regular migrant through eastern North and South Dakota, suggesting that there is some as yet unknown breeding area. The species has been recorded in migration, more often in fall, in Wyoming, Colorado, Nebraska, Kansas, Oklahoma, and Texas.
Observers at Aweme, Manitoba, in 38 years recorded it only twice. Another observer at Eastend, southwestern Saskatchewan, recorded it for the first time on September 21, 1937, after at least twenty years of continuous observation.
On the basis of such information it seems probable that the species is slowly spreading its breeding range westward.