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. In the winter months it is to be met with throughout the more temperate portions of North America, in Mexico, Central America, and Northern South America. Dr. Woodhouse mentions finding this species very abundant especially among the wooded banks of watercourses throughout Texas, New Mexico, and the Indian Territory. Mr. March states that this Hawk is a permanent resident in the island of Jamaica, more frequently found among the hills than on the plains, and has been known to breed there. It is a visitant of Cuba. Dr. Cooper thinks they are not very common in Washington Territory, though, as they are found there throughout the summer, they undoubtedly breed there. In August, 1855, Dr. Cooper shot one of a small family of young that had but recently left their nest. They migrate southward in winter, and are abundant in California in October and November.