~ 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). yggs 
2.37 X 1.72. Hab. 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?. Darker colored: Top of head usually with dusky prevailing, 
often uniform dusky, lighter tail-bands bluish gray, and 
usually narrower than dusky interspaces. Adulé 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. 
fi. Lower parts with white prevailing, or at least equal in 
extent to the dusky. Male: Wing 13.35-14.25 (13.54), 
tail 8.00-9.00 (8.49), culmen .86-.93 (.90), 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 2.34 1.77. Hab. Northern Europe and 
