A History of North American Birds, Land Birds. Volume 3. Robert Ridgway

not at all difficult to distinguish from columbarius. Now, however, I incline strongly to the theory that it represents merely the light form of the central prairie regions, of the common species; since its characters seem to be so analogous to those of the races of Buteo borealis and Bubo virginianus of the same country. It is doubtful whether some very light-colored adult males, supposed to belong to columbarius, as restricted, should not in reality be referred to this race, as the adult plumage of the male. But having seen no adult males from the region inhabited by the present bird obtained in the breeding-season, I am still in doubt whether the present form ever assumes the blue plumage.

      As regards the climatic or regional modifications experienced by the Falco lithofalco on the American continent, the following summary of facts expresses my present views upon the subject. First: examples identical in all respects, or at least presenting no variations beyond those of an individual character, may be found from very widely separated localities; but the theory of explanation is, that individuals of one race may become scattered during their migrations, or wander off from their breeding-places. Second: the Atlantic region, the region of the plains, and the region of the northwest coast, have each a peculiar race, characterized by features which are also distinctive of races of other birds of the same region, namely, very dark—the dark tints intensified, and their area extended—in the northwest coast region; very light—the light markings extended and multiplied—in the middle region; and intermediate in the Atlantic region.

      Habits. The distribution of the well-known Pigeon Hawk is very nearly coextensive with the whole of North America. It is found in the breeding-season as far to the north as Fort Anderson, on the Anderson and McKenzie rivers, ranging even to the Arctic coast. Specimens were taken by Mr. Ross at Lapierre House and at Fort Good Hope. Several specimens were taken by Mr. Dall at Nulato, where, he states, it is found all the year round. They were also taken by Bischoff at Kodiak. During the breeding-season it is found as far south as Nova Scotia, New Brunswick, and the northern portions of Maine, and probably Vermont and New York. It is abundant on the Pacific coast.