2 BULLETIN 17 0, UNITED STATES NATIONAL MUSEUM 



Falco rusticolus. The British Ornithologists' Union List (1915) recog- 

 nizes two species, Hierojalco gyrfalco and H. islandus, each with two 

 subspecies, only three of the four forms being listed as British. But 

 Witherby's Handbook (1924) includes the three British forms as sub- 

 species under rusticolus. Peters's Check-List (1931) names five races 

 from different parts of the world, all as subspecies of rusticolus. Only 

 three of these are included as North American in the latest American 

 Ornithologists' Union Check-List (1931). I examined the large series 

 of specimens in the Museum of Comparative Zoology, on which Mr. 

 Peters based his conclusions, and I believe his treatment of the group 

 is as nearly correct as our present knowledge permits. 



The distribution given in the A. O. U. Check-List (1931), which is 

 practically the same as that given by Peters (1931), is, I believe, sub- 

 stantially correct, but I doubt if candicans breeds regularly anywhere 

 on the North American Continent; the Asiatic form, uralensis, very 

 likely does extend its breeding range into extreme northern Alaska 

 but probably not onto the southern Bering Sea coast. Apparently all 

 the gyrfalcons that breed regularly on the North American mainland 

 are referable to obsoleius. The breeding records of the white gyrfal- 

 cons in Labrador and Ungava, mentioned below, doubtless represent 

 cases of casual breeding far south of the normal breeding range. 



The white gyrfalcon {Falco rusticolus candicans) breeds in northern 

 Greenland at least as far south as latitude 76° N. and perhaps farther 

 on the west coast; on the east coast it may breed farther south than 

 on the west coast, as the east coast is much colder. In southern 

 Greenland, at least from Disco Island southward, the breeding birds 

 are darker, but just what their status is has not yet been definitely 

 determined. Dr. Walter Koelz (1929), who went to Greenland on one 

 of the MacMillan expeditions, brought back a fine series of these fal- 

 cons; these are deposited in the University of Michigan collection, 

 which now contains 88 Greenland gyrfalcons. In this large series he 

 found specimens from various points in southern Greenland, from lati- 

 tude 73° southward on the west coast, which compare favorably with 

 the Iceland bird (islandus), with the Scandinavian bird (rusticolus), 

 and with the dark North American bird (obsoletus). These puzzling 

 variations are probably due to interbreeding with birds from Labra- 

 dor, or possibly from Iceland. Such strong-flying and wide-ranging 

 birds could easily fly from either of these places to Greenland and 

 might become established there. Ptarmigans regularly migrate be- 

 tween Greenland and Labrador, and the short distance could easily 

 be covered by a gyrfalcon. It is conceivable that obsoletus, the dark 

 Labrador race, might regularly migrate to southern Greenland and, 

 by interbreeding with the light northern race, produce a variety of 

 intermediates. 



