Hirundo horreorum.
Sp. Char. Tail very deeply forked; outer feathers several inches longer than the inner, very narrow towards the end. Above glossy blue, with concealed white in the middle of the back. Throat chestnut; rest of lower part reddish-white, not conspicuously different. A steel-blue collar on the upper part of the breast, interrupted in the middle. Tail-feathers with a white spot near the middle, on the inner web. Female with the outer tail-feather not quite so long. Length, 6.90 inches; wing, 5.00; tail, 4.50.
Hab. Whole of the United States; north to Fort Rae, Slave Lake; Greenland; south in winter to Central America and West Indies; Panama (Lawr.); Plateau of Mexico (breeds, Sumichrast); Veragua, Chiriqui (Salvin). Not found at Cape St. Lucas. South America?
In young birds, the frontal chestnut band is maller and less distinct.
It is still a question whether a South American resident species (H. erythrogaster) is identical or not. The only two specimens of the latter (21,007 and 21,008, Vermejo, Feb., 1860; C. Wood) have a very much less violaceous upper plumage than North American examples, the blue above having even a greenish tinge. They are moulting, unfortunately, so that they cannot be satisfactorily compared; except in the respect pointed out, however, they appear to be identical with North American examples.
The European H. rustica is perfectly distinct, though closely allied. It differs essentially from the American H. horreorum in much longer outer
tail-feathers, and in having a very broad, continuous collar of steel-blue across the jugulum, entirely isolating the chestnut of the throat; the abdomen appears to be much more whitish than in the American species.
Many specimens of H. horreorum show a continuous collar, but then the two lateral crescents are but just barely connected. In No. 2,191 ♀, Carlisle, Penn., May, there is an indication of as broad a collar as in the European species; but the area, though sharply bounded, is not uniformly black, being much mixed centrally with light rufous.
Specimens of H. horreorum from both coasts of North America appear to be perfectly identical.