FALCONID JS — THE FALCONS. 



287 



Measurements. 



A large collection of specimens of this race presents a series connecting 

 horealis with the black form known as " ccdunts " ; every possible condition 

 between the two being indicated in the range of individual variation. The 

 lightest styles as distinguished from var. horealis always have the tibiae 

 barred with rufous ; the crissum, also, is generally barred, on the throat 

 the blackish-brown predominates, and the tail has more or less perfect bars 

 to the roots of the feathers ; generally, however, these are merely indicated 

 by projections from the shafts. 



The extreme condition of this is the melanistic form which Mr. Cassin 

 described as " Bttteo calurus" ; the darkest example of which (5,481, Peta- 

 luma, Cal. ; E. Samuels) is entirely blackish-brown, wings and scapulars 

 with feathers somewhat paler at tips ; breast inclining to dark sepia-brown, 

 the feathers with black shaft-streaks ; tibial feathers faintly tipped with pale 

 grayish-brown ;. lower tail-coverts tipped and barred with rufous ; upper tail- 

 coverts deep rufous barred with black ; tail deep chestnut-rufous, the sub- 

 terminal black band very broad, and anterior to this are nine or ten imperfect 

 narrower black bands. 



These fuliginous examples have always a more or less appreciably lighter 

 pectoral area, corresponding to the white of this region seen in the lighter 

 styles. 



Of this race, almost each individual has its own characteristic markings, 

 and scarcely two are to be found alike in a very large series from Western 

 jSTorth America. All the specimens from the Eocky Mountains to the 

 Pacific, and from the table-lands of Mexico, as well as from Cuba and 

 Jamaica, are referrible to this variety, although we are not aware that in 

 the latter reoion the bird ever becomes black. In the latter island this 

 species (as is also the case with many other birds) seems to be remarkably 

 subject to albinism. In the peninsula of Lower California it is replaced 

 by the var. lucasanus, and in Central America by the very different var. 

 costaricensis ; from both of whicli it may be distinguished by the numerous 

 transverse rufous bars crossing the posterior under parts, which character 

 serves also to distinguish the lightest examples from the eastern typical 

 horealis. 



A specimen (50,761 ; Colonel Grayson) from the Socorro Island, S. W. 

 Mexico, is like some Port Tejon specimens. 



