Jan., 1909. Birds of Illinois and Wisconsin — Cory. 477 



recorded from Dakota and Minnesota (W. W. Cooke, Bird Migration 

 Miss. Val., 1888, p. 118). 



The following brief synopsis of the two forms may be useful: 



Gyrfalcon. Falco rusticolus gyrfalco (Linn.). 



Size of Gray Gyrfalcon; back, grayish, the barring irregular, 

 sometimes wanting; tail, like back, showing imperfect pale bars; 

 head, streaked; under parts, heavily streaked with whitish and brown- 

 ish gray. 



Specimen taken at Vermillion, Dakota, Oct. 21, 1880, by Dr. 

 Agersborg (Cooke). 



Black Gyrfalcon. Falco rusticolus obsoletus (Gmel.). 



Size about the same as preceding; general color above and below, 

 dusky or dusky slate color, without bars; the dark under parts more 

 or less marked with buff. 



"Has been taken in Minnesota a few times as a rare winter visi- 

 tant. A specimen has been examined by Mr. Ridgway." (Cooke.) 



168. Falco mexicanus ScHLEG. 



Prairie Falcon. 



Distr.: Western species, ranging from the plains to the Pacific, 

 south to Mexico; accidental as far east as Illinois. 



Adult: First primary, notched; second primary, slightly notched 

 about one and a quarter inches from tip ; second primary, very slightly 

 longer than third; upper plumage, grayish brown, the feathers edged 

 and more or less barred with buff or pale rusty brown; tail, pale 

 brownish gray, most of the feathers barred with brownish white ; 

 primaries, grayish brown, with numerous white bars on the inner webs 

 which do not reach the shaft of the feathers and the inner portion 

 of these white marks tinged with pale brown; under parts, dull white, 

 streaked and spotted with dark brown, heaviest on sides; a brown 

 stripe on sides of throat. 



Immature: Upper plumage, grayish brown, the feathers edged 

 with rusty brown; under parts, bufiy white or pale buff, streaked, 

 with dusky; axillars, plain dusky, without bars. 



Male: Length, 16.75 to 18; wing, 11.50 to 12.50; tail, 7; tarsus, 

 about 2. 



Female: Length, 18 to 19.50; wing, 12.50 to 14; tail, 8.50; tar- 

 sus, 2.25. 



This species is of accidental occurrence in Illinois. Ridgway 

 writes (Orn. of Illinois, p. 431) : "A specimen was obtained at Rock 

 Island by Mr. I. D. Sargent of Philadelphia, and by him presented to 



