A History of North American Birds, Land Birds. Volume 3

Spencer Fullerton Baird, Thomas Mayo Brewer, Robert Ridgway

A History of North American Birds; Land Birds; Vol. 3 of 3

RAPTORES. 1 —The Birds of Prey

The group of birds usually known as the Raptores, or Rapacious Birds, embraces three well-marked divisions, namely, the Owls, the Hawks, and the Vultures. In former classifications they headed the Class of Birds, being honored with this position in consequence of their powerful organization, large size, and predatory habits. But it being now known that in structure they are less perfectly organized than the Passeres and Strisores, birds generally far more delicate in organization, as well as smaller in size, they occupy a place in the more recent arrangements nearly at the end of the Terrestrial forms.

The complete definition of the order Raptores, and of its subdivisions, requires the enumeration of a great many characters; and that their distinguishing features may be more easily recognized by the student, I give first a brief diagnosis, including their simplest characters, to be followed by a more detailed account hereafter.

Common Characters. Bill hooked, the upper mandible furnished at the base with a soft skin, or “cere,” in which the nostrils are situated. Toes, three before and one behind. Raptores.

Strigidæ. Eyes directed forwards, and surrounded by radiating feathers, which are bounded, except anteriorly, by a circle or rim of differently formed, stiffer feathers. Outer toe reversible. Claws much hooked and very sharp. Legs and toes usually feathered, or, at least, coated with bristles. The Owls.

Falconidæ. Eyes lateral, and not surrounded by radiating feathers. Outer toe not reversible (except in Pandion). Claws usually hooked and sharp, but variable. Head more or less completely feathered. The Hawks.

Cathartidæ. Eyes lateral; whole head naked. Outer toe not reversible; claws slightly curved, blunt. The Vultures.

The preceding characters, though purely artificial, may nevertheless serve to distinguish the three families of Raptores belonging to the North American Ornis; a more scientific diagnosis, embracing a sufficient number of osteological, and accompanying anatomical characters, will be found further on.

The birds of prey—named Accipitres by some authors, and Raptores or Rapaces by others, and very appropriately designated as the Ætomorphæ by Professor Huxley—form one of the most strongly characterized and sharply limited of the higher divisions of the Class of Birds. It is only recently, however, that their place in a systematic classification and the proper number and relation of their subdivisions have been properly understood. Professor Huxley’s views will probably form the basis for a permanent classification, as they certainly point the way to one eminently natural. In his important paper entitled “On the Classification of Birds, and on the Taxonomic Value of the Modifications of certain Cranial Bones observable in that Class,”2 this gentleman has dealt concisely upon the affinities of the order Raptores, and the distinguishing features of its subdivisions. In the following diagnoses the osteological characters are mainly borrowed from Professor Huxley’s work referred to. Nitzsch’s “Pterylography”3 supplies such characters as are afforded by the plumage, most of which confirm the arrangement based upon the osteological structure; while important suggestions have been derived from McGillivray’s “History of British Birds.”4 The Monographs of the Strigidæ and Falconidæ, by Dr. J. J. Kaup,5 contain much valuable information, and were they not disfigured by a very eccentric system of arrangement they would approach nearer to a natural classification of the subfamilies, genera, and subgenera, than any arrangement of the lesser groups which I have yet seen.

The species of this group are spread over the whole world, tropical regions having the greatest variety of forms and number of species. The Strigidæ are cosmopolitan, most of the genera belonging to both continents. The Falconidæ are also found the world over, but each continent has subfamilies peculiar to it. The Cathartidæ are peculiar to America, having analogous representatives in the Old World in the subfamily Vulturinæ belonging to the Falconidæ, The Gypogeranidæ are found only in South Africa, where a single species, Gypogeranus serpentarius (Gmel.), sole representative of the family, is found.

As regards the comparative number of species of this order in the two continents, the Old World is considerably ahead of the New World, which might be expected from its far greater land area. 581 species are given in Gray’s Hand List,6 of which certainly not more than 500, probably not more than 450, are valid species, the others ranking as geographical races, or are synonymous with others; of this number about 350 nominal species are accredited to the Old World. America, however, possesses the greatest variety of forms, and the great bulk of the Old World Raptorial fauna is made up chiefly by a large array of species of a few genera which are represented in America by but one or two, or at most half a dozen, species. The genera Aquila, Spizætus, Accipiter, Haliætus, Falco, Circus, Athene, Strix, and Buteo, are striking examples. As regards the number of peculiar forms, America is considerably ahead.

Family STRIGIDÆ.—The Owls

Char. Eyes directed forward, and surrounded by a radiating system of feathers, which is bounded, except anteriorly, by a ruff of stiff, compactly webbed, differently formed, and somewhat recurved feathers; loral feathers antrorse, long, and dense. Plumage very soft and lax, of a fine downy texture, the feathers destitute of an after-shaft. Oil-gland without the usual circlet of feathers. Outer webs of the quills with the points of the fibres recurved. Feathers on the sides of the forehead frequently elongated into ear-like tufts; tarsus usually, and toes frequently, densely feathered. Ear-opening very large, sometimes covered by a lappet. Œsophagus destitute of a dilated crop; cœca large. Maxillo-palatines thick and spongy, and encroaching upon the intervening valley; basipterygoid processes always present. Outer toe reversible; posterior toe only about half as long as the outer. Posterior margin of the sternum doubly indented; clavicle weak and nearly cylindrical, about equal in length to the sternum. Anterior process of the coracoid projected forward so as to meet the clavicle, beneath the basal process of the scapula. Eggs variable in shape, usually nearly spherical, always immaculate, pure white.

The Owls constitute a very natural and sharply limited family, and though the species vary almost infinitely in the details of their structure, they all seem to fall within the limits of a single subfamily.

They have never yet been satisfactorily classified, and all the arrangements which have been either proposed or adopted are refuted by the facts developed upon a close study into the true relationship of the many genera. The divisions of “Night Owls,” “Day Owls,” “Horned Owls,” etc., are purely artificial. This family is much more homogeneous than that of the Falconidæ, since none of the many genera which I have examined seem to depart in their structure from the model of a single subfamily, though a few of them are somewhat aberrant as regards peculiarities in the detail of external form, or, less often, to a slight extent, in their osteological characters, though I have examined critically only the American and European species; and there may be some Asiatic, African, or Australian genera which depart so far from the normal standard of structure as to necessitate a modification of this view. In the structure of the sternum there is scarcely the least noticeable deviation in any genus7 from the typical form. The appreciable differences appear to be only of generic value, such as a different proportionate length of the coracoid bones and the sternum, and width of the sternum in proportion to its length, or the height of its keel. The crania present a greater range of variation, and, if closely studied, may afford a clew to a more natural arrangement than the one which is here presented. The chief differences in the skulls of different genera consist in the degree of pneumaticity of the bones, in the form of the auricular bones, the comparative length and breadth of the palatines, and very great contrasts in the contour. As a rule, we find that those skulls which have the greatest pneumaticity (e.g. Strix and Otus) are most depressed anteriorly, have the orbital septum thicker, the palatines longer and narrower, and a deeper longitudinal median valley on the superior surface, and vice versa.

The following classification is based chiefly upon external characters; but these are in most instances known to be accompanied by osteological peculiarities, which point to nearly the same arrangement. It is intended merely as an artificial table of the North American genera, and may be subjected to considerable modification in its plan if exotic genera are introduced.8

Genera and Subgenera

A. Inner toe equal to the middle in length; inner edge of middle claw pectinated. First quill longer than the third; all the quills with their inner webs entire, or without emargination. Tail emarginated. Feathers of the posterior face of the tarsus recurved, or pointed upwards.

1. Strix. No ear-tufts; bill light-colored; eyes black; tarsus nearly twice as long as middle toe; toes scantily haired. Size medium. Ear-conch nearly as long as the height of the skull, with an anterior operculum for only a portion of its length; symmetrical.

B. Inner toe decidedly or much shorter than the middle; inner edge of middle claw not pectinated. First quill shorter than the third; one to six outer quills with their inner webs emarginated. Tail rounded. Feathers of the posterior face of the tarsus not recurved but pointed downwards.

I. Nostril open, oval, situated in the anterior edge of the cere, which is not inflated.

a. Cere, on top, equal to, or exceeding, the chord of the culmen; much arched. Ear-conch nearly as long as the height of the skull, with the operculum extending its full length; asymmetrical.

2. Otus. One or two outer quills with their inner webs emarginated. With or without ear-tufts. Bill blackish; iris yellow. Size medium.

Ear-tufts well developed; only one quill emarginated … Otus.

Ear-tufts rudimentary; two quills emarginated … Brachyotus.

b. Cere, on top, less than the chord of the culmen; gradually ascending basally, or level (not arched). Ear-conch nearly the height of the skull, with the operculum extending only a part of its full length, or wanting entirely.

† Anterior edge of the ear-conch with an operculum; the two ears asymmetrical.

3. Syrnium. Five to six outer quills with their inner webs emarginated. Top of cere more than half the culmen. Without ear-tufts. Bill yellow; iris yellow or black. Size medium or large.

Six quills emarginated; toes densely feathered, the terminal scutellæ concealed; iris yellow. Size very large … Scotiaptex.

Five quills emarginated; toes scantly feathered, the terminal scutellæ exposed; iris black. Size medium … Syrnium.

4. Nyctale. Two outer quills with inner webs emarginated. Top of cere less than half the culmen, level. Without ear-tufts. Bill yellow or blackish; iris yellow. Size small.

†† Anterior edge of the ear-conch without an operculum. The two ears symmetrical. Tail slightly rounded, only about half as long as the wing.

5. Scops. Two to five quills with inner webs emarginated; second to fifth longest. Bill weak, light-colored. Ear-conch elliptical, about one-third the height of the head, with a slightly elevated fringed anterior margin. Size small; ear-tufts usually well developed, sometimes rudimentary.

6. Bubo. Two to four outer quills with inner webs emarginated; third to fourth longest. Bill robust, black. Ear-conch elliptical, simple, from one third to one half the height of the skull. Size large. Ear-tufts well developed or rudimentary.

Ear-tufts well developed. Two to three outer quills with inner webs emarginated; lower tail-coverts not reaching end of the tail. Toes covered with short feathers, the claws exposed, and bill not concealed by the loral feathers … Bubo.

Ear-tufts rudimentary. Four outer quills with their inner webs emarginated; lower tail-coverts reaching end of the tail. Toes covered with long feathers, which hide the claws, and bill nearly concealed by the loral feathers … Nyctea.

††† Similar to the last, but the tail graduated, nearly equal to the wing.

7. Surnia. Four outer quills with inner webs emarginated. Third quill longest. Bill strong, yellow; ear-conch simple, oval, less than the diameter of the eye. Size medium; no ear-tufts.

II. Nostril, a small circular opening into the surrounding inflated membrane of the cere. Ear-conch small, simple, oval, or nearly round, without an operculum.

First quill shorter than the tenth.

8. Glaucidium. Third to fourth quills longest; four emarginated on inner webs. Tarsus about equal to the middle toe, densely feathered. Tail much more than half the wing, rounded. Bill and iris yellow. Size very small.

9. Micrathene. Fourth quill longest; four emarginated on inner webs. Tarsus a little longer than middle toe, scantily haired. Tail less than half the wing, even. Bill light (greenish ?); iris yellow. Size very small.

First quill longer than sixth.

10. Speotyto. Second to fourth quills longest; three emarginated on inner webs. Tarsus more than twice as long as middle toe, closely feathered in front to the toes, naked behind. Tail less than half the wing, slightly rounded. Bill yellowish; iris yellow. Size small.

In their distribution, the Owls, as a family, are cosmopolitan, and most of the genera are found on both hemispheres. All the northern genera (Nyctea, Surnia, Nyctale, and Scotiaptex), and the majority of their species, are circumpolar. The genus Glaucidium is most largely developed within the tropics, and has numerous species in both hemispheres. Otus brachyotus and Strix flammea are the only two species which are found all over the world,—the former, however, being apparently absent in Australia. Gymnoglaux, Speotyto, Micrathene, and Lophostrix are about the only well-characterized genera peculiar to America. Athene, Ketupa, and Phodilus are peculiar to the Old World. The approximate number of known species (see Gray’s Hand List of Birds, I, 1869) is about two hundred, of which two, as stated, are cosmopolitan; six others (Surnia ulula, Nyctea scandiaca, Glaucidium passerinum, Syrnium cinereum, Otus vulgaris, and Nyctale tengmalmi) are found in both halves of the Northern Hemisphere; of the remainder there are about an equal number peculiar to America and the Old World.

As regards the distribution of the Owls in the Nearctic Realm, a prominent feature is the number of the species (eighteen, not including races) belonging to it, of which six (Micrathene whitneyi, Nyctale acadica, Syrnium nebulosum, S. occidentale, Scops asio, and S. flammeola) are found nowhere else. Speotyto cunicularia and Bubo virginianus are peculiarly American species found both north and south of the equator, but in the two regions represented by different geographical races. Glaucidium ferrugineum and G. infuscatum (var. gnoma) are tropical species which overreach the bounds of the Neotropical Realm,—the former extending into the United States, the latter reaching to, and probably also within, our borders. Of the eighteen North American species, about nine, or one half (Strix flammea var. pratincola, Otus brachyotus, O. vulgaris var. wilsonianus, Syrnium cinereum, Nyctale acadica, Bubo virginianus, and Scops asio, with certainty, and Nyctea scandiaca var. arctica, and Surnia ulula var. hudsonia, in all probability), are found entirely across the continent. Nyctale tengmalmi, var. richardsoni, and Syrnium nebulosum, appear to be peculiar to the eastern portion,—the former to the northern regions, the latter to the southern. Athene cunicularia var. hypugaea, Micrathene whitneyi, Glaucidium passerinum var. californicum, Syrnium occidentale, and Scops flammeola, are exclusively western, all belonging to the southern portion of the Middle Province and Rocky Mountain region, and the adjacent 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.