FALCO. 



245 



width to the darker ones ; darker and lighter bands on tail 

 usually very sharply contrasted, the former often slate- 

 gray, the latter pale ash-gray or dull whitish ; flanks and 

 thighs never very heavily banded or spotted with slaty, 

 but always more or less marked with this color. Young : 

 Dark stripes of lower parts usually decidedly narrower than 

 white interspaces; upper parts in general usually much 

 spotted with whitish or light buffy, in addition to the 

 lighter margins (often conspicuous) to the feathers; outer 

 webs of quills more or less distinctly spotted with whitish 

 toward base. Male: Length about 20.00-21.00, wing 

 13.40-15.00 (14.10), tail 8.00-9.30 (8.51), culmen .88-.98 

 (.90), tarsus 2.10-2.65 (2.40), middle toe 1.80-2.20 (1.96). 

 Female: Length about 22.00-24.50, wing 15.25-16.50 

 (15.76), tail 9.10-10.50 (9.72), culmen .95-1.10 (1.01), tar- 

 sus 2.30-2.60 (2.46), middle toe 1.98-2.15 (2.08). Eggs 

 3.37 X 1-72. Sab. Extreme northern portions of Europe 

 (except Scandinavia), Asia, and North America, including 

 Iceland and southern Greenland; south, in winter, to 

 northern border of United States. 



354. F. rusticolus (Linn.). Gray Gyrfalcon. 

 e a . Darker colored : Top of head usually with dusky prevailing, 

 often uniform dusky, lighter tail-bands bluish gray, and 

 usually narrower than dusky interspaces. Adult with an- 

 terior upper parts (back, scapulars, and wing-coverts) 

 rather indistinctly barred with bluish gray, often nearly 

 plain dusky ; flanks heavily banded or spotted with dusky, 

 and thighs heavily barred with slaty (the white ground- 

 color tinged with bluish gray posteriorly). Young : Dark 

 stripes of lower parts usually about equal in width to 

 white interspaces, sometimes much broader (under parts 

 sometimes plain dusky) ; upper surface of tail never (?) 

 continuously banded with whitish, sometimes almost plain, 

 or, if barred at all, the bars interrupted, much narrower 

 than the dark interspaces, and never (?) approaching white 

 in color; upper parts usually plain grayish brown, the 

 feathers more or less distinctly margined with paler, but 

 usually with little if any whitish spotting. 

 P- Lower parts with white prevailing, or at least equal in 

 extent to the dusky. Male: Wing 13.75-14.25 (13.97), 

 tail 8.00-8.75 (8.26), culmen .90-.92 (.96), tarsus 2.30- 

 2.50 (2.35), middle toe 1.90-2.00 (1.96). Female : Wing 

 15.25-16.00 (15.52), tail 9.00-10.50 (9.82), culmen 1.00- 

 1.10 (1.03), tarsus 2.25-2.65 (2.48), middle toe 2.05-2.15 

 (2.10). Eggs 2.31 X 1-76. Hab. Northern Europe and 



