A very remarkable characteristic of the Owls is the fact that many of the species exist in a sort of _dimorphic_ condition, or that two plumages sufficiently unlike to be of specific importance in other cases belong to one species. It was long thought that these two phases represented two distinct species; afterwards it was maintained that they depended on age, sex, or season, different authors or observers entertaining various opinions on the subject; but it is now generally believed that every individual retains through life the plumage which it first acquires, and that young birds of both forms are often found in the same nest, their parents being either both of one form, or both of the other, or the two styles paired together.[12] The normal plumage, in these instances, appears to be grayish, the pattern distinct, the markings sharply defined, and the general appearance much like that of species which do not have the other plumage. The other plumage is a replacing of the grayish tints by a bright lateritious-rufous, the pencillings being at the same time less well defined, and the pattern of the smaller markings often changed. This condition seems to be somewhat analogous to _melanism_ in certain _Falconidæ_, and appears to be more common in the genera _Scops_ and _Glaucidium_ (in which it affects mainly the tropical species), and occurs also in the European _Syrnium aluco_. As studied with relation to our North American species, we find it only in _Scops asio_ and _Glaucidium ferrugineum_. The latter, being strictly tropical in its habitat, is similarly affected throughout its range; but in the former we find that this condition depends much upon the region. Thus neither Dr. Cooper nor I have ever seen a red specimen from the Pacific coast, nor do I find any record of such an occurrence. The normal gray plumage, however, is as common throughout that region as in the Atlantic States. In the New England and Middle States the red plumage seems to be more rare in most places than the gray one, while toward the south the red predominates greatly. Of over twenty specimens obtained in Southern Illinois (Mt. Carmel) in the course of one winter, only one was of the gray plumage; and of the total number of specimens seen and secured at other times during a series of years, we can remember but one other gray one. As a parallel example among mammals, Professor Baird suggests the case of the Red-bellied Squirrels and Foxes of the Southern States, whose relationships to the more grayish northern and western forms appear to be about the same as in the present instance. GENUS STRIX, SAVIGNY. _Strix_, SAVIGNY, 1809 (_nec_ LINN. 1735). (Type, _Strix flammea_, LINN.) _Stridula_, SELLYS-LONGCH, 1842. _Eustrinx_, WEBB & BERTH. 1844. _Hybris_, NITZSCH. [Illustration: =6885= ⅓ _Strix pratincola._]