BUTEO CALURUS. 583 



the cotton-woods of the Truckee and Carson Valleys, where we found it 

 quite unsuspicious and easily killed. During the summer it was nuicli less 

 abundant in the lower valleys than Swainson's Hawk, but it was more 

 common on the mountains, particularly in the pine forests. On the Wali- 

 satch, we saw several of its nests on tall pine trees or on ledges of tlu; cliiTs, 

 most of them being inaccessible, in which respect this species differs con- 

 s])icuonslv from the B. suabisoui, which in the same region was found to 

 build its nest on the top of the scrub-oaks or in the small aspens, within 

 easy reach. 



The series of specimens in the collection exhibits the usual individual 

 variation so remarkable to the western birds of this species, there being 

 examjdes so light-colored as to be scarcely distinguishable from the typical 

 eastern B. borealis, while one is of an almost uniform deep sooty-black, the 

 others beinsf variously intermediate. As was the case Avith D. swainsoni, the 

 light and dark individuals were often found paired.' 



List of specimens. 



i;!2, 9 0(1. (melanotic, very blaclj; Big Bend of the Truckee (Camp 12), Nevada, 

 August 17, ISCT. L'.^A— .J4— UU (molting)- Bill, slate-black, the basal half of tlie 

 lower niiuulible bluisb-slate; cere, dull .vellowish green, purest on top; ri(!tus, more 

 yellow; iris, muddy naples-ydlow ; tarsi and toes, dull pale greenisb-yellow ; claws 

 black. 



337, 9 ad (melanotic, rufous breasted style); Genoa, Nevada, November 29, 18G7. 

 23i— 55— 17— 14— l^^j5 — 2— 0^— .".t. Weight, 3J pounds. Bill, dull black, passing into 

 pale bluish biisally ; cere and rictus, light dull ashy-green; iris, deep hazel ; tarsi and 

 toes jiale (lull na))lesyellow ; claws, black. 



347, <J (id.; Truckee Heservation, December 10, 18(;7. 21-J— 51}— 1»5— LiJ— U— 

 (?)— 9— 5. Weight, 2 pounds. Bill, dull black, fading into dull light bluish basally; 

 cere and rictus, dull greenish-yellow; iris, deep ligiit hazel; tarsi and toes, very dull 

 light chrome-yellow, deeper beneath. 



SrA.^a'd.; same locality, December 11, 1.S07. 2M— 49— 15^— 12-j— 1/,,— (f/— 9^ 

 —:>.!,. Weight, 2i pounds. Bill, black, fading basally into light horn-drab; basal half 

 of the lower mandible, pale blue; cere and rictus, clear light yellowish-green; iris, 



'There being many who yet hold the old belief that this dark phase, foiuid in so 

 many sjjecics of Talconida', is in some manner dependent on ape, we wish to imi)res3 

 our readers with the fact that it is a purely indiridual corulition, entirely iiuhjundent of 

 age, sex, or season; it is properly styled melanism, and is analogous to the condition of 

 erylhrixm in certain owls. In every American species which has this fuliginous plu- 

 mage, the dark birds are dusky /rom //if Hcs/ h;;; while those in light plumage never 

 assume the dark dress. This is probably the case with the Old World species also. 



