166 FALCONS, HAWKS, EAGLES, ETC. 



3. Slaty bluish above. 



4. Top of head darker than back anatum, p. 167. 



4'. Top of head and back uniform pealei, p. 168. 



1'. Two primaries with inner webs cut out. 



2. Tarsus not decidedly longer than middle toe. 



3. Middle tail feathers crossed by not more than four blackish or five 



light bands. 

 4. Inner webs of quills distinctly barred or spotted. 



columbarius, p. 168. 

 4'. Inner webs of quills not distinctly barred or spotted. 



suckleyi, p. 169. 

 3'. Middle tail feathers crossed by 5 darker and 6 lighter bands. 



richardsonii, p. 169. 



2'. Tarsus decidedly longer than middle toe. 

 3. Side of head with one horizontal stripe. 



fusco-ccerulescens, p. 170. 

 3'. Side of head with two black vertical stripes. 



4. Darker. Eastern United States .... sparverius, p. 170. 

 4'. Paler. Western United States .... deserticola, p. 171. 



Subgenus Hierofalco. 



Tarsus feathered two thirds of the way down in front and on sides, the 

 edges of the feathering meeting on the posterior side. 



854. Falco rusticolus Linn. GRAY GYRFALCON. 



Adults. Top of head largely streaked with white ; anterior upper parts 

 barred with grayish or whitish and darker ; tail strongly banded ; flanks 

 and thighs more or less marked with slaty. Young : upper parts much 

 spotted with white or buffy ; under parts with dark stripes usually nar- 

 rower than white interspaces. Male: length 20-21, wing 14.10, tail 8.51, 

 bill .90, tarsus 2.40. Female : length 22.00-24.50, wing 15.76, tail 9.72, 

 bill 1.01, tarsus 2.46. 



Distribution. Extreme northern portions of Europe (except Scandi- 

 navia), Asia, and North America, including Iceland and southern Green- 

 land ; south in winter to northern border of United States. 



The gyrfalcons are so rare in the United States that, as Dr. Fisher 

 says, a man may consider himself fortunate if he sees one in a life- 

 time. 



355. Palco mexicanus Schlegel. PRAIRIE FALCON. 



Adult male. Under parts and nuchal collar white, sides of head with 

 dark patches ; median under parts lightly streaked or spotted, and flanks 

 heavily spotted or blotched with dusky ; upper parts pale clay brown, 

 usually tinged with rusty and indistinctly but broadly barred with pale 

 clay color or dull buffy anteriorly, and with pale bluish gray posteriorly. 

 Adult female : upper parts dull clay brown, feathers edged with rusty 

 brown or dull whitish, paler toward tail ; tail tipped with whitish and 

 lighter on outer edges of feathers. Young : upper parts grayish brown, 

 feathers edged with light rusty ; under parts buffy with broader dusky 

 streaks ; dark flank patch larger and more uniform than in the adult, and 

 axillars unbroken dusky. Male : length 17-18,' wing 11.60-12.50, tail 

 3.40-7.50, bill .70-75. Female: length 18.50-20.00, wing 13.25-14.30, 

 tail 8-9, bill .85-.90. 



Distribution. United States, from the eastern border of the Plains to 



