JAN., 1909. BIRDS OF ILLINOIS AND WISCONSIN CORY. 149 



First primary, pale brown, with numerous bands on inner web; 

 length, usually under 19 (some females are longer); upper plumage, 

 grayish brown. Falco mexicanus. 



Prairie Falcon. 

 See No. 168. 



Length, always over 19; under tail coverts, spotted, or washed 

 with dusky ; upper parts, grayish, barred and marked with white ; 

 under parts, white, streaked and spotted with blackish. 



Falco rusticolus. 

 Gray Gyrfalcon. 

 See No. 167. 



SECTION 2. Third primary, longest; face, bare. 



Throat, white or buff; upper surface of tail, grayish brown, with 

 numerous bars; three outer primaries, emarginate, or notched. 



Buteo swains oni. 

 Swainson's Hawk. 

 See No. 160. 



SECTION 3. Fourth primary, longest; upper tail coverts, white. 



Upper tail coverts, white; under surface of tail, white or pale 

 mfous, with several bands of dark brown. Circus hudsonius. 



Marsh Hawk. 

 See No. 154. 



SECTION 4. Fourth primary, longest; upper tail coverts, not white. 



Upper surface of tail, bright rufous brown, with or without bands 

 (adult). Buteo borealis, atid races. 



Red-tailed Hawk. 

 See Nos. 158, isSa, is8b, 1580. 



Upper surface of inner webs of outer tail feathers, barred with 

 brown and white ; tail feathers, more or less tinged with pale rufous ; 

 primaries, not tinged with rufous (immature). 



Buteo borealis, and races. 

 Red-tailed Hawk. 

 See Nos. 158, isSa, isSb, i^Sc. 



Upper surface of inner web of outer tail feathers, barred with 

 brown and white ; tail feathers, more or less tinged with pale rufous ; 

 primaries, more or less tinged with rufous (immature). 



Buteo lineatus. 

 Red-shouldered Hawk. 

 See No. 159. 



