61 FALCONID^E. 



to R. swainsoni. A second undoubtedly Argentine example is that pro- 

 cured 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, pi. Ixii.). 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- 

 rum ped Shrikes (Lanius ludovicianns ex cubit oroides] built also imme- 

 diately 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 speci- 

 mens 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." 



