In Chile and Brazil (Western ?) we find a form resembling the last in some respects, but differing in points of almost specific value. It differs from all the other American members of the genus in having the tail continuously rufous to the extreme tip, the black zone being considerably narrower than the terminal rufous, the lateral tail-feather immaculate rufous, etc. The grayish of the head is much darker and more slaty than in the var. australis. This is, without doubt, the Falco cinnamominus of Swainson, the specimens in the collection corresponding exactly with the description by that author.
The rufous patch on the crown must not be too much considered, as it is of all characters perhaps the most treacherous, though its presence or absence is in a measure characteristic of the several varieties. Neither does the exact number of spots on the lateral tail-feather prove sufficiently constant to serve as a character in which the least reliance can be placed, though Swainson attaches considerable value to it. I have found that, besides varying almost with the individual, in some specimens the feathers of opposite sides did not correspond.
About two hundred and fifty specimens form the basis of the following synopsis.
A. Tail tipped with white; outer tail-feathers (one or more) variegated.
a. ♂. Head above, and wings, fine bluish-ash; usually one tail-feather only (the outer) variegated.
1. Vertex with a conspicuous patch of rufous. ♂. Black zone of the tail 1.00 in width; breast strongly tinged with ochraceous; spots of black on the breast or sides circular. ♀. Above fulvous-rufous, the whole breast and sides with longitudinal dashes of a lighter tint of the same. Hab. Continent of North America north of Panama (except Caribbean and Gulf coast) … var. sparverius.
2. Vertex with only a trace of rufous, or none at all. ♂. Black zone of tail only .60 in width; breast nearly pure white; spots of black usually only on the sides, elliptical. ♀. Above vinaceous-rufous; longitudinal markings beneath deeper brown. Hab. Continent of South America (except North Atlantic and Caribbean coast) … var. australis.[64]
b. ♂. Head above, and wings, dark bluish-plumbeous; several outer tail-feathers variegated.