24-i NORTH AMERICAN BIRDS. 



Genus FALCO Linn^us. (Page 224, pi. LXXII., figs. 1-5 ; pi. LXXIII., figs. 1-3.) 



Species. 



a}. Only one quill (the outermost) with inner web emarginated near tip ; first quill 

 longer than fourth. 

 6\ Tarsus decidedly longer than middle toe (without claw) ; first quill shorter 

 than third. 

 &. Tarsus densely feathered in front and on sides for the upper two- 

 thirds, the edges of the feathering meeting on the posterior side. 

 Nest usually on clifi's. Eggs 2-4, about 2.30 X 1-75, varying from 

 pale cinnamon or tawny to buffy, more or less distinctly sprinkled, 

 speckled, or marbled with deeper cinnamon-brown — sometimes 

 almost uniformly cinnamon-color. (Subgenus Hierofalco Guvier.) 

 d}. Lower tail-coverts immaculate white, the thighs also usually im- 

 maculate; prevailing color of whole plumage white. Adult: 

 Top of head and hind-neck usually narrowly strea,ked with 

 dusky, but often immaculate ; rest of upper parts more or less 

 barred, or transversely spotted, with slate-dusky; lower parts 

 usually immaculate, or without well-defined markings. Young: 

 Upper parts with longitudinal spots or stripes of dusky (this 

 less slaty than in adult) ; lower parts usually distinctly striped. 

 Male: Length about 21.00-22.50, wing 14.00-14.75 (14.49), tail 

 8.50-9.50 (8.94), culmen .90-.98 (.92), tarsus 2.30-2.50 (2.43), 

 middle toe 1.95-2.05 (1.98). Female : Length about 23.00-24.00, 

 wing 15.50-16.50 (16.00), tail 9.00-10.00 (9.49), culmen .95-1.08 

 (1.03), tarsus 2.30-2.50 (2.47), middle toe 2.05-2.15 (2.09). Eggs 

 2.26 X 1-27. Hab. Circumpolar regions, breeding in Greenland, 

 northeastern (and other?) portions of Arctic America, Com- 

 mander Islands, etc. 



353. F. islandus Brunn. White Gyrfalcon. 

 d\ Lower tail-coverts always more or less marked with dusky ; upper 

 parts with little if any white, except, sometimes, on top of head 

 and hind-neck. Adult with upper parts banded with dusky 

 and bluish gray (sometimes uniform dusky anteriorly), the 

 flanks and thighs barred, banded, or transversely spotted with 

 dusky. Young without transverse bars on upper parts (ex- 

 cept sometimes on tail), and lower parts with all the markings 

 longitudinal. 

 e\ Lighter colored : Top of head much streaked with white, often 

 with white prevailing, the lighter tail-bands usually whitish 

 and nearly as broad as the darker interspaces. Adult, with 

 anterior upper parts everj'where more or less distinctly 

 barred with very pale grayish, grayish white, or buffy 

 whitish, these lighter bars sometimes nearly equal in 



