Occasionally an immense multitude of Hawks soaring high in the air, and in company, has been observed. This curious phenomenon has been seen by our friends, Professor Baird, of the Smithsonian Institution, Washington city; Dr. Hoy, of Racine, Wisconsin; and by ourselves. It occurs in autumn, and is probably incidental to migration; but its exact character and object is unknown, and involves an interesting inquiry. It is necessarily temporary, as the procuring of suitable food by such a large number of rapacious birds would be impossible. In the western and northern regions of North America, the birds of this family are particularly worthy of the attention of the traveller and naturalist, and would undoubtedly well repay him in the discovery of unknown species. This is the case also in the States of Florida and Texas, to the latter of which, very probably, some of the many Mexican species are visitors, that have not yet been noticed. In Oregon and Russian-America, there are also very probably species which have not been recognized as inhabitants of this continent, though well known as birds of Northern Asia, and others entirely unknown to naturalists. B. Doubtful and obscure species which have been described as inhabiting North America. 1. Falco americanus. Gm., Syst. Nat., I. p. 257. (1788.) The Black-cheeked Eagle. Pennant, Arctic Zoology, I. p. 227. “With a dusky and blue-bill; yellow cere; head, neck and breast of a deep ash-color, each cheek marked with a broad black bar passing from the corner of the mouth beyond the eyes; back, belly, wings, and tail, black; legs yellow; feathered below the knees. Is about the size of the last (the Golden Eagle) North America,” (Pennant, as above.) Of this bird, Gmelin gives a short abstract of Pennant’s description, and applies a scientific name. Naturalists relying solely on that abstract, have erroneously considered the species meant as the Golden Eagle (_A. chrysaetus_), and the name _Falco americanus_ has accordingly been usually quoted as a synonyme. Though “feathered below the knees” is somewhat indefinite, yet, taken in connexion with “legs yellow,” it is clear that this cannot be the Golden Eagle, which has the tarsus densely feathered. There is no North American species known to which the original description applies. 2. Falco candidus. Gm., Syst. Nat., I. p. 258. (1788.) The Louisiana White Eagle. Lath., Syn., I. p. 36. Du Pratz, Hist. Louisiane, II. p. 109. Falco conciliator. Shaw, Gen. Zool. Aves., VII. p. 77. (1809.) White; tips of the wings black. Smaller than the Golden Eagle.