It appears from what these authorities say (l. c. p. 268) that a young specimen procured by Hudson at Conchitas in 1860, and referred by Messrs. Salvin and Sclater with doubt to B. albicaudatus, really belongs to B. swainsoni. A second undoubtedly Argentine example is that procured by Mr. Withington and now figured.
Like other Buzzards, B. swainsoni varies much in plumage, and occasionally assumes a melanistic form, under which it was described and figured by Sclater in 1858 as Buteo fuliginosus (cf. P. Z. S. 1858, p. 356, and Trans. Zool. Soc. vol. iv. p. 267, pl. lxii.). Mr. Gurney is of opinion that d’Orbigny’s Buteo unicolor is also referable to this form of B. swainsoni (cf. Ibis, 1889, p. 134).
A well-known writer on North-American birds (Capt. C. E. Bendire) gives the following account of the nesting of Buteo swainsoni in Arizona:—
“This species is by far the commonest Hawk in the vicinity of Fort Huachuca, and a resident throughout the year. Lieutenant Benson found not less than forty-one of their nests containing eggs between May 14 and June 18, 1887. These were all placed in low mesquite trees and bushes, from 3 to 15 feet from the ground. Only six of these nests contained three eggs each, twenty-one nests contained two eggs, the remaining fourteen but a single egg. Many of the latter were undoubtedly laid by birds that had been robbed before, especially where the same nest was used again, which was frequently the case, and a few were uncompleted sets. Two eggs is the usual number laid by these birds, in Arizona at least. The nests were bulky platforms, composed of sticks of various sizes, with but a slight depression in the centre, and sparingly lined with a few bunches of dried grass. Lieutenant Benson writes me that after the Arkansas King-birds (Tyrannus verticalis, Say) began to build he invariably found one of their nests in any tree that contained a Swainson’s Hawk’s nest. In one case, a pair of these birds had placed their nest directly under, and but 8 or 9 inches from that of the Hawk. A pair of White-rumped Shrikes (Lanius ludovicianns excubitoroides) built also immediately below one of these Hawk’s nests.
“When not closely looked at, many of the eggs of Swainson’s Hawk appear to be unspotted, but on careful examination there are in reality but very few that are immaculate. Out of a series of sixty-nine specimens sent by Lieutenant Benson there are but three unspotted ones. The ground-colour of these eggs when fresh is a very distinct greenish white, which in course of time fades into a dull yellowish white, even if the eggs are not exposed to light. They are more or less heavily spotted and blotched, varying in colour from burnt-umber to tawny olive, and in some of the lighter coloured specimens from a French grey to a drab-grey. Their shape ranges from a short ovate to an oval, and they average about 2·23 by 1·71 inches in length and width.”
[296.] BUTEO ALBICAUDATUS (Vieill.).
(WHITE-TAILED BUZZARD.)
Buteo albicaudatus, Durnford, Ibis, 1877, p. 187 (Buenos Ayres); Döring, Exp. al Rio Negro, p. 51 (Rio Negro); Withington, Ibis, 1888, p. 469 (Lomas de Zamora). Tachytriorchis albicaudatus, Sharpe, Cat. B. i. p. 162. Buteo pterocles, Scl. et Salv. Nomencl. p. 119; Barrows, Auk, 1884, p. 109 (Gualeguaychú); White, P. Z. S. 1882, p. 622 (Buenos Ayres).
Description.—Above greyish black, scapulars and upper wing-coverts ferruginous; rump and tail white, the latter with a broad black subapical band, and with slight narrow transverse slaty bars: beneath, throat black, abdomen white, flanks more or less barred with brown; bill black; feet dirty yellow: whole length 21·0 inches, wing 18·0, tail 8·0. Female similar, but rather larger.
Hab. Southern and Central America.