The greatest difficulty in the study of the Owls of North America will be found in the intimate resemblance that a few species bear to others of Europe and Asia, and, we may add, in the examination of the birds which we have given in the preceding pages as varieties of the Great-horned Owl (_Bubo virginianus_). The variations that we have noticed, and especially those of color, may be ascertained by subsequent observation to be so uniform and constant as to constitute specific distinction, though at present we cannot so regard them. In the Owls of other countries there are several groups in which it is very difficult to determine the species, on account of their resemblance to each other. This is especially the case with the small species of the genus _Scops_, which inhabit India and other countries of Asia; and there are, too, many of the birds of this genus, of all countries, that are exceedingly perplexing. In fact, we would hardly recommend a student in natural history to begin General Ornithology with the Owls. With this family we conclude the rapacious Birds. BUTEO INSIGNATUS.—(Cassin.) The Brown Buzzard. PLATE XXXI.—Adult Male and Young Female. One of the most remarkable facts in the geographical distribution of the birds of western and northwestern North America is, that many species extend their range in northern latitudes almost or quite to the shores of the Atlantic ocean, while not a single instance is on record of the same species having been observed in either of the middle or southern States of the Union. The Magpie, which on the Pacific is commonly found southwardly as far as Mexico, has been noticed by Dr. Hoy, at Racine, in the State of Wisconsin. The Lark Bunting (_Emberiza grammaca_), another western bird, has also been ascertained by the same gentleman to be abundant in the State just mentioned; and the only specimen that we have ever seen of the Stone Chat of America (_Saxicola œnanthoides_), a bird discovered some years since on the coast of Oregon, was obtained in the vicinity of Halifax, Nova Scotia. Many instances tending to demonstrate this extensive and remarkable migration might be produced, but we have unfortunately to acknowledge ourselves unable to offer a theory or even hypothesis attempting to account for it, and must regard the facts as remaining among many in natural history with which naturalists are for the present under the necessity of resting, without inference or application to any established general principles. Important results will yet reward American naturalists who may engage in this interesting field of scientific research.