Part 23

CLASSIFICATION.

One great advantage of the study of birds is that the amount of facts to be learnt in anatomy is far less than with some other groups. They are wonderfully uniform in structure. There is less difference in structure between an ostrich and a humming-bird than between, say, a lizard and a crocodile. Though this may be gratifying to the student of birds who is content with a broad knowledge of anatomical fact, it has its disadvantages--very distinct disadvantages--to those who want to arrange and classify the species. As there are computed to be over eleven thousand different kinds of birds, it is clear that an arrangement of some kind is wanted; we must have an artificial brain in which to store the characters of each bird in their proper place. But before we can consider this it is necessary to consider first what place birds as a whole occupy in Nature. It used to be thought that warm-blooded birds ought to be put near to the warm-blooded mammals. But it is now the general opinion that, as we have before pointed out in relation to certain details of structure, their proper place is in the neighbourhood of the reptiles. In fact they are regarded as a separate division of an order of vertebrated animals which has received the name of Sauropsida, which signifies ‘lizard-like’ animals.

Now, as to these eleven thousand, how are they to be divided? To this simple question innumerable answers have been given--it is hardly an exaggeration to say as many answers as there are ornithologists. Every part of the body has had its turn in affording a base for a classificatory scheme. At first, and with the older generation, it was bill and claw; then came a period of bones; later the muscles were held to be all-important; at present the fashion is in favour of taking all characters into consideration, which is clearly a more reasonable way of looking at the matter. The reason for the divergences of opinion--which implies great difficulty in the subject--is that birds are so modern a race. They are now at their heyday of development. By-and-by, when gaps appear in the now serried ranks, classification will be an easier matter; for classification, after all, is an artificial, unnatural sort of thing, if we believe in a gradual modification of species out of pre-existing species. It is not too much to say that, the more perfect our scheme of classification, the greater our ignorance of the group classified. If the only birds known to science were a Hornbill, a Duck, and a Crow, together with a few of the immediate allies of each, we could easily sort them. But there are so many intermediate forms which absolutely decline to fit accurately into any system. Then the would-be systematist has to distinguish between those characters which imply a deep-seated relationship and those which are only due to similar needs. The aim of classification is, of course, to indicate real relationship, not merely to pigeon-hole in a convenient way. Real relationship is often masked by superficial differences. For instance, the common blindworm of our hedgerows is not, as might be thought, a snake, but a lizard; it appears to be unlike the lizard in having no legs, and to be so far a snake. Indeed, the terror inspired by this peaceful reptile must stand it in good stead with any except human foes. But its whole anatomy is built upon the lizard, and not upon the snake, plan. We disregard, therefore, in a scheme of classification the likeness to a snake, remembering that in Nature, as in morals, appearances are apt to be deceptive. The owls, among birds, are believed by many to offer an instance of the same kind of deception. By all the older systematists, and by many of the more modern, they are placed with the hawks in one group. No doubt the owls bear a certain likeness to the hawks. They have formidable claws and a hooked and powerful beak; they kill their prey; and only differ superficially in that they love the darkness, while the hawks hunt by day. Now, in certain details of anatomy, particularly in the windpipe and the muscles, the owls are much more like that division of birds which includes the goatsuckers. The mention of this latter family brings us face to face with another difficulty. If the superficial likeness of the owls to the hawks is to be distrusted, as merely due to a similar mode of life, and therefore to the development of certain structures which are in direct relation to that mode of life, how about the superficial likeness of the owls to the goatsuckers, which is almost as well marked as to the hawks? In Australia and other parts of the East there are two genera of goatsuckers which have received the names of Podargus and Batrachostomus. These birds are wonderfully like owls. They have the same brown-and-grey and soft plumage; their flight is equally noiseless--and, altogether, anyone who saw the living Cuvier’s Podargus recently on view at the Zoological Gardens might well be pardoned for thinking it an owl. The fact is that we must be careful not to be prejudiced in any direction. Superficial similarities may or may not go with real likeness. Speaking generally, one should be disposed to lay greatest stress upon characters which have no obvious relation to mode of life as likely to be of the most use in indicating blood relationship. It is easier, however, to lay down general principles of this kind than to apply them to birds. As has been already mentioned, birds are so uniform in anatomy that in such characters as brain, lungs, and other internal organs which are not so directly under the immediate influence of their surroundings, there is but little difference. Such characters afford no help to the systematist. We are obliged, therefore, to rely upon other and really less important points.

In most books upon ornithology--in this one, for instance--the scheme of classification is set forth in the shape of a list beginning with one particular group and ending with another. This is merely due to the physical properties of sheets of paper. A linear scheme is really an impossibility; to represent classification properly we want a solid diagram, showing how from a root-stock branches arose and pushed their way in every direction. Another defect of the linear scheme is that we must begin somewhere and end somewhere. In this book we begin with the Passeres and end with the Parrots; others start with the Accipitres, in spite of the protest of Michelet against placing the cowardly, flat-headed, stupid hawks at the summit of bird creation. It doesn’t matter where we begin or where we end as long as we carefully bear in mind that a linear classification is only a convenient way of briefly stating certain facts, and that it does not pretend to be a copy of Nature. An alternative method of expressing the facts of structure in space of two dimensions is the Stammbaum, originally made in Germany; but this inevitable tree of life is open to the serious objection of undue dogmatism; and besides, it must be inaccurate, as it is not in three dimensions. A given naturalist may have strong reasons for believing, let us say, that the Struthious birds represent the lowest bird stock, from which arose in a regular series of branches, independently, and alternately from one side or the other, the various groups into which we divide the class in the present book; if so, then the Stammbaum is easily constructed. But the general consensus of opinion is that the inter-relationships of the different groups cannot be expressed with so much simplicity. It is clear that, in any case, the most modified offshoots must occupy the highest branches of the tree, and that we may in a linear scheme conveniently begin or end with them. But it is impossible to arbitrate as to which group is the most specialised. It is, on the whole, agreed that the Ostrich tribe have retained more primitive characters than other birds; but is the elaborate voice-mechanism of the Nightingale, or the almost human intelligence of the Raven or Parrot, to rank first as evidence of high position, i.e. specialisation, remoteness from the original stock? This is a matter about which everybody can legitimately have an opinion; and we cannot at present formulate a creed--for those, that is to say, who are acquainted with the facts.

The scheme that I adopt here is the same as that which Mr. Hudson uses in the pages which follow; it is the plan followed in the B.O.U. list, and approved by most ornithologists in this country as a convenient working outline. I have added to it the fossil groups, and those groups which do not occur in Great Britain. The main scheme is that of Dr. Gadow, used in his valuable account of the anatomy of birds in Bronn’s ‘Klassen und Ordnungen des Thierreichs.’ There is no deep-seated and mysterious reason for my placing Parrots at the end of the Aves Carinatæ: it is simply sheer inability to place them anywhere in particular.

CLASS. AVES.

SUB-CLASS I. Archæornithes (contains genus Archæopteryx only). SUB-CLASS II. Neornithes. Division i. Neornithes Ratitæ. Order i. Ratitæ (contains Struthio, Rhea, Dinornis, &c.). Order ii. Stereornithes (contains a few fossil genera, Gastornis, Dasornis, &c.). Division ii. Neornithes Odontolcæ. Order i. Hesperornithes (the extinct Hesperornis and Enaliornis). Division iii. Neornithes Carinatæ. Order i. Ichthyornithes (fossil Ichthyornis only). Order ii. Passeres (thrushes, swallows, flycatchers, tits, &c.). Order iii. Picariæ (rollers, cuckoos, hornbills, woodpeckers, swifts, colies, trogons, goatsuckers, kingfishers). Order iv. Striges (owls). Order v. Accipitres (hawks, eagles, American vultures, &c.). Order vi. Steganopodes (cormorants, pelicans, solan geese, frigate bird). Order vii. Herodiones (herons, storks, ibis, spoonbills). Order viii. Odontoglossi (flamingoes). Order ix. Anseres (screamers, ducks, geese). Order x. Columbæ (doves). Order xi. Pterocletes (sand-grouse). Order xii. Gallinæ (curassows, megapodes, pheasants, grouse, Opisthocomus, &c.). Order xiii. Tinamidæ (tinamous). Order xiv. Fulicariæ (rails, coots). Order xv. Alectorides (cranes, bustards, Cariama, &c.). Order xvi. Limicolæ (plovers, snipe, knots, &c.). Order xvii. Gaviæ (gulls, skuas). Order xviii. Pygopodes (auks, divers, grebes). Order xix. Sphenisciformes (penguins). Order xx. Tubinares (petrels, albatross). Order xxi. Psittaci (parrots).

It will be noticed that, out of these twenty-one groups into which we may divide the Neornithes Carinatæ of Gadow, only three are not represented in Great Britain, viz. the Sphenisciformes, Psittaci, and Tinamiformes. So that the student of bird anatomy in this country has plenty of chance of making himself acquainted with the main outlines of structure of the entire class of living birds. Out of the thirty-two minor divisions of these birds, no fewer than twenty-one are to be met with in these islands; and of those that are not, some are quite easy to get hold of--a parrot, for instance.

Missel-Thrush, or Stormcock.

Turdus viscivorus.

Upper parts ash-brown; under parts white, faintly tinged with yellow, marked with numerous black spots; under wing-coverts white; three lateral tail feathers tipped with greyish white. Length, eleven inches.

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There are six British thrushes. Of these the missel-thrush and blackbird are residents throughout the year; the song-thrush is also found with us at all seasons, and is a winter songster, but many birds migrate; the ring-ouzel is a summer visitor; the redwing and fieldfare are winter visitors.

The missel or mistletoe thrush, or stormcock, is the largest, exceeding the fieldfare, which comes next in size, by at least an inch in length and two inches in spread of wings. This species possesses in a marked degree all the characters that everywhere distinguish the true thrushes, which are world-wide in their range. Theirs is a modest colouring:--olive-brown above, paler and spotted below; a loud and varied song, and harsh cry; a statuesque figure; rapid, startled movements on the ground, with motionless intervals, when the bird stands with head and beak much raised, in an attitude denoting intense attention; and, finally, a free, strong, undulating flight.

The missel-thrush inhabits almost the whole of the British Islands, and is most abundant in Ireland. Throughout England and Wales he is fairly common, less common in Scotland, and becoming rarer the farther north we go. He is found in all woods and plantations, but is most partial to wooded parks, orchards, and gardens, which afford him food and shelter throughout the year. He is the hardiest of our vocalists, and is better known as a winter than a summer songster. His song may be heard in the autumn, but from midwinter until spring his music is most noteworthy. Its loudness and wild character give it a wonderful impressiveness at that season of the year. He is not of the winter singers that wait for a gleam of spring-like sunshine to inspirit them, but is loudest in wet and rough weather; and it is this habit and something in the wild and defiant character of the song, heard above the tumult of nature, which have won for him the proud name of stormcock.

This thrush is an early breeder, and pairs about the beginning of February. The birds, after mating, are exceedingly pugnacious, and attack all others, large or small, that approach the chosen nesting-site. The nest is not often made in evergreens, to which blackbirds and song-thrushes are so partial; as a rule, a deciduous tree--oak, elm, or beech--is made choice of, and the nest may be at any height, from a few feet above the ground to the highest part of a tall tree; and as it is built so early in the year, when trees are leafless, it forms a most conspicuous object. Furthermore, the missel-thrush, a shy and wary bird at other times, becomes strangely trustful, and even careless, when nesting, and often builds in the neighbourhood of a house, or in an isolated tree at the roadside. When building and breeding the birds are silent, except when the nest is threatened with an attack, when they become clamorous and bold beyond most species in defence of their eggs or nestlings.

The nest is large and well made, outwardly of dry grass, moss, and other materials, woven together; it is plastered with mud inside, and thickly lined with fine dry grass. The four eggs vary in ground-colour from bluish white to pale reddish brown, and are spotted, blotched, and clouded, with various shades of purple, brown, and greyish under-markings. Two or three broods are reared in the season.

At the end of June the missel-thrushes begin to unite in small parties numbering a dozen to twenty birds, and to range over the open country, seeking their food in the pastures and turnip-fields, and on moors and commons. Where the birds are abundant much larger congregations are seen. In Ireland I have seen them in August in flocks of about a hundred birds. They do not keep close together, as is the manner of starlings and finches, but fly widely scattered, and alight at a distance apart, a flock of fifty to a hundred birds sometimes occupying half an acre or more ground. They then look very large and conspicuous, scattered over the green grass, standing erect and motionless, or hopping about in their wild, startled manner. These flocks diminish in number as the season progresses, and finally break up about midwinter.

In autumn the missel-thrushes devour the yew-berries, and the fruit of the rowan and service trees; later in the year they feed on the glutinous berries of the mistletoe, on haws and ivy-berries, and other wild fruits; but their food for the most part consists of earthworms, snails, grubs, and insects of all kinds.

Throstle, or Song-Thrush.

Turdus musicus.

FIG. 18.--SONG-THRUSH. ¼ natural size.

Upper parts olive-brown, throat white in the middle; sides of neck and under parts ochreous yellow spotted with dark brown; under wing-coverts pale orange-yellow. Length, nine inches.

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The protest and recommendation implied by the use of the first name at the head of this article may be futile; but it is impossible not to feel and to express regret that so good and distinctive and old a name for this familiar bird should have been replaced by a name which is none of these things. Song-thrush is an unsuitable name, for the very good reason that we have several thrushes, all of them songsters. By most persons the bird is simply called ‘thrush,’ which is neither better nor worse than ‘song-thrush.’

The throstle is one of the smaller members of the genus, being about a third less in size than the noble stormcock. In form, colouring, motions, language, and habits, he is a very thrush. It cannot be said that his music is the best--that, for instance, it is finer than that of the blackbird. The two songs differ in character; both are good of their kind, neither perfect. The throstle is, nevertheless, in the very first rank of British melodists, and it is often said of him that he comes next to the nightingale. The same thing has been said of other species, tastes differing in this as in other matters. It is worth remarking that most persons would agree in regarding the nightingale, song-thrush, blackbird, blackcap, and skylark, as our five finest songsters, and that these all differ so widely from each other in the character of their strains that no comparison between them is possible, and there is no rivalry.

The only species which may be called the rival of the song-thrush is the missel-thrush, as their music has a strong resemblance. That of the stormcock has a wonderful charm in the early days of the year, when it is a jubilant cry, a herald’s song and prophecy, sounding amidst wintry gloom and tempest. Heard in calm and genial weather in spring, the throstle is by far the finer songster. His chief merit is his infinite variety. His loudest notes may be heard half a mile away on a still morning; his lowest sounds are scarcely audible at a distance of twenty yards. His purest sounds, which are very pure and bright, are contrasted with various squealing and squeaking noises that seem not to come from the same bird. Listening to him, you never know what to expect, for his notes are delivered in no settled order, as in some species. He has many notes and phrases, but has never made of them one completed melody. They are snatches and portions of a melody, and he sings in a scrappy way--a note or two, a phrase or two, then a pause, as if the singer paused to try and think of something to follow; but when it comes it has no connection with what has gone before. His treasures are many, but they exist jumbled together, and he takes them as they come. As a rule, when he has produced a beautiful note, he will repeat it twice or thrice; on this account Browning has called him a ‘wise bird,’ because he can

recapture The first fine careless rapture.