A History of North American Birds, Land Birds. Volume 3. Robert Ridgway
parts of Mexico, excepting the more generally distributed Speotyto cunicularia, var. hypogæa, before mentioned. Anomalies in regard to the distribution of some of the species common to both continents, are the restriction of the American representative of Glaucidium passerinum to the western regions,9 and of Strix flammea to the very southern and maritime portions of the United States, the European representatives of both species being generally distributed throughout that continent. On the other hand, the northwest-coast race of our Scops asio (S. kennicotti) seems to be nearly identical with the Japanese S. semitorques (Schlegel), which is undoubtedly referrible to the same species.
As regards their plumage, the Owls differ most remarkably from the Hawks in the fact that the sexes are invariably colored alike, while from the nest to perfect maturity there are no well-marked progressive stages distinguishing the different ages of a species. The nestling, or downy, plumage, however, of many species, has the intricate pencilling of the adult dress replaced by a simple transverse barring upon the imperfect downy covering. The downy young of Nyctea scandiaca is plain sooty-brown, and that of Strix flammea immaculate white.
In many species the adult dress is characterized by a mottling of various shades of grayish mixed with ochraceous or fulvous, this ornamented by a variable, often very intricate, pencilling of dusky, and more or less mixed with white. As a consequence of the mixed or mottled character of the markings, the plumage of the Owls is, as a rule, difficult to describe.
In the variations of plumage, size, etc., with differences of habitat, there is a wide range, the usually recognized laws10 applying to most of those species which are generally distributed and resident where breeding. Of the eight species common to the Palæarctic and Nearctic Realms, all but one (Otus brachyotus) are modified so as to form representative geographical races on the two continents. In each of these cases the American bird is much darker than the European, the brown areas and markings being not only more extended, but deeper in tint. The difference in this respect is so tangible that an experienced ornithologist can instantly decide to which continent any specimen belongs. Of the two cosmopolitan species one, Otus brachyotus, is identical throughout; the other is modified into geographical races in nearly every well-marked province of its habitat. Thus in the Palæarctic Realm it is typical Strix flammea; in the Nearctic Realm it is var. pratincola; while Tropical America has at least three well-marked geographical races, the species being represented in Middle America by the var. guatemalæ, in South America by var. perlata, and in the West Indies by the var. furcata. The Old World has also numerous representative races, of which we have, however, seen only two, namely, var. javanica (Gm.), of Java, India, and Eastern Africa, and var. delicatula (Gould) of Australia, both of which we unhesitatingly refer to S. flammea.11
On the North American continent the only widely distributed species which do not vary perceptibly with the region are Otus brachyotus and O. vulgaris (var. wilsonianus). Bubo virginianus, Scops asio, and Syrnium nebulosum all bear the impress of special laws in the several regions of their habitat. Starting with the Eastern Province, and tracing either of these three species southward, we find it becoming gradually smaller, the colors deeper and more rufous, and the toes more scantily feathered. Scops asio reaches its minimum of size and maximum depth of color in Florida (var. floridana) and in Mexico (var. enano).
Of the other two I have not seen Florida specimens, but examples of both from other Southern States and the Lower Mississippi Valley region are much more rufous, and—the S. nebulosum especially—smaller, with more naked toes. The latter species is darkest in Eastern Mexico (var. sartori), and most rufescent, and smallest, in Guatemala (var. fulvescens). In the middle region of the United States, Scops asio (var. maccalli) and Bubo virginianus (var. arcticus) are more grayish and more delicately pencilled than from other portions. In the northwest coast region they become larger and much more darkly colored, assuming the clove-brown or sooty tints peculiar to the region. The var. kennicotti represents S. asio in this region, and var. pacificus the B. virginianus. The latter species also extends its range around the Arctic Coast to Labrador, and forms a northern littoral race, the very opposite extreme in color from the nearly albinescent examples of var. arcticus found in the interior of Arctic America.
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.
6885 ⅓
Strix pratincola.
Gen. Char. Size medium. No ear-tufts; facial ruff entirely continuous, very conspicuous. Wing very long, the first or second quill longest, and all without emargination. Tail short, emarginated. Bill elongated, compressed, regularly curved; top of the cere nearly equal to the culmen, straight, and somewhat depressed. Nostril open, oval, nearly horizontal. Eyes very small. Tarsus nearly twice as long as the middle toe, densely clothed with soft short feathers, those on the posterior face inclined upwards; toes scantily bristled; claws extremely sharp and long, the middle one with its inner edge pectinated. Ear-conch nearly as long as the height of the head, with an anterior operculum, which does not extend its full length; the two ears symmetrical?
The species of Strix are distributed over the whole world, though only one of them is cosmopolitan. This is the common Barn Owl (S. flammea), the type of the genus, which is found in nearly every portion of the world, though in different regions it has experienced modifications which constitute geographical
This case of the restriction of the American representative of a European or Western Palæarctic species to the western half of the continent has parallel instances among other birds. The American form of
Instances of a similar relation between the plants of the Western Province of North America and those of Europe, and more striking likeness between the flora of the Eastern Region and that of Eastern Asia, are beautifully explained in Professor Gray’s interesting and instructive paper entitled “Sequoia, and its History,” an address delivered at the meeting of the American Association for the Advancement of Science, at Dubuque, Iowa, August, 1872. The poverty in the species of tortoises, and richness in lizards, and the peculiarities of the ichthyological fauna, as well as absence of forms of Western North America and Europe, compared with Eastern North America and Eastern Asia, afford other examples of parallelism in other classes of the Animal Kingdom.
See Baird, Am. Journ. Arts and Sciences, Vol. XLI, Jan. and March, 1866; Allen, Bull. Mus. Comp. Zoöl. Cambridge, Vol. II, No. 3; and Ridgway, Am. Journ. Arts and Sciences, Vols. IV and V, Dec., 1872, and Jan., 1873.
For diagnoses of these geographical races of
See Allen, Bull. Mus. Comp. Zoöl., Cambridge, Vol. II, No. 3, pp. 338, 339, where these plumages are discussed at length.