b. Tarsus long; equal to middle toe and half claw; entirely bare. Tail considerably forked, about equal to closed wing. Color green above; white beneath … Callichelidon.[62]
Genus PROGNE, Boie.
Progne, Boie, Isis, 1826, 971. (Type, Hirundo purpurea vel subis, L.)—Baird, Birds N. Am. 1858, 314.
Gen. Char. Body stout. Bill robust, lengthened; lower or commissural edge of maxilla sinuated, decidedly convex for basal half, then as concave to the tip, the lower mandible falling within its chord. Nostrils superior, broadly open, and nearly circular, without any adjacent membrane, the edges rounded. Legs stout. Tarsus equal to middle toe without claw; the joint feathered; lateral toes about equal; the basal joint of the middle toe half free internally, rather less so externally. Claws strong, much curved. Nest in hollow trees. Eggs white.
The species of this genus are the most powerful and robust of the Swallows. Some are entirely glossy-black, others whitish below. The following
diagnosis will show the relationship of the several forms usually recognized as distinct species:—
Species and Varieties.
P. subis. Above lustrous blue-black; beneath lustrous blue-black or brownish-gray, uniform, or with the abdomen and crissum white, or whitish. Females always with the throat and jugulum gray.
A. Adult males entirely steel-blue.
a. Females and young males with the abdomen pure white.