206 
There is considerable confusion regarding the relationship of the 
various forms of Gyrfalcon, and some of the generally recognized sub- 
species may eventually turn out to be but individual variations or phase 
plumages, and even both American species may possibly be united under 
one, as there is a most perplexing amount of intergradation between them. 
353. White Gyrfalcon. Falco istandus. L, 22. A. very large "Falcon, mostly pure 
-white, with amah, sharp markings of brown or black. 
Distinctions. The general whiteness. It may be pure white with only small, sparse, 
scattered, dark Seeks on the wing tips, wings, or back; or the dark may even be predominant 
on wings and back, and sharply shaft-streak the crown (Figure 230 a). The lack of mark- 
ings on the undertail coverts separates this species from similarly coloured individuals of 
Grey Gyrfalcon. 
Field Marks. Long, sharp wings, and flight as a Falcon. Large size and white 
coloration as the White Gyrfalcon. 
Nesting. On rocky cliffs. 
Distribution. The Arctic regions of both hemispheres. Occurring in Canada across 
the Arctic, west to Dolphin and Union straits. Taken south occasionally on the southern 
British Columbia coast, and on the prairies as far south as the International Boundary. 
354. Gyrfalcon (Including Grey and Black Gyrfalcons). Falco rusticolus. 
L, 20. A very large Falcon, similar to the White Gyrfalcon, but much darker, the markings 
of greyish, brown, or even near-black, being more extensive. The back may be solidly 
coloured, or more or less variegated with white; the crown is dark, sharply streaked with 
white or solidly dark (Figure 230 b and c) . The breast may be white sparsely streaked 
or nearly solidly dark brown. 
Distinctions. Recognized as a GyrfalcoD by its pointed wings, toothed bill, and large 
size. Separated from the White Gyrfalcon by darker coloration, especially the under tail 
coverts. The lightest phase of this species may approach closely in colour to the darkest 
of the preceding species. In general, however, in the White Gyrfalcon, white greatly pre- 
dominates, but with this bird the white and dark are about equally extensive, or the dark 
predominates. 
Field Marks. A very large Falcon, almost solidly dark; may be light in colour some- 
times, but never with white predominating. 
Nesting. On cliffs or in trees. 
Distribution. The Arctic regions of both hemispheres. In Canada, across the con- 
tinent, occurring occasionally in late autumn or winter almost anywhere in the Dominion. 
There are more records for Alberta than elsewhere in southern localities, and those of 
British Columbia are confined to the southern coast. 
SUBSPECIES. The Gyrfalcon shows a remarkable amount of variation, and scarcely 
two specimens are exactly alike. Judging from captive birds this does not seem due to 
age or sex, nor is it easily correlated with distribution, yet the American representatives 
of the species have been divided into three geographical races, based on colour. The light- 
est, the Grey Gyrfalcon Falco rusticolus rusticolus, approaches darker individuals of the 
White Gyrfalcon, but can be separated by its shaft-streaked or barred undertail coverts. 
The upper parts are solid lightish brown, or brown or greyish, barred with white. The 
flanks are striped or barred and the tail somewhat barred. The crown, broadly streaked 
with light and dark in approximately equal proportions (Figure 230 b) is perhaps the 
best criterion of the subspecies. The Gyrfalcon, having no distinctive common name, 
Falco rusticolus gyrfalco is the next darkest. The dark body markings are confluent ,and 
more extensive, showing more dark than light. The crown is practically solidly dark 
(Figure 230 c). Most of the prairie records seem to be of this form, but either of the two 
can be expected on the coast of southern British Columbia. The darkest form, the Black 
Gyrfalcon Falco rusticolus obsoletus, seems confined to our north Atlantic coast. 
355. Prairie Falcon. Falco mexicanus. L, about 18. Like a pale or faded Peregrine. 
Much like the illustiation of the juvenile of that species, Plate XXVII B, but more white 
below. 
Distinctions. Recognizable as a Falcon by toothed bill (Figure 229) and pointed 
wing (Figure 228). Rather variable in size, but, considering above distinctions, likely to 
be confused only with the Peregrine Falcon. Similar in colour pattern to that species, but 
exhibits little change due to age. In any plumage the darker colours are in faded or light 
