Part 5

The brain of birds is large in proportion to the body, thus contrasting with that of the unintelligent reptile. From some tables on the matter which have been published, it appears that, if weight of brain goes for anything, the goldfinch is one of the most intelligent of birds. The weight of its brain is one-fourteenth of the entire weight of the body. The most unintelligent of all is the domestic fowl, whose body is 412 times heavier than its brain. The size of brain, however, seems to be largely a matter of the size of the bird: generally speaking, the smaller birds have heavier brains, and _vice versâ_. One might have expected something from the apparently intelligent Parrot; but the brain of the ‘Amazon’ is only one forty-second part of the weight of its body. Even the cruel and bloodthirsty Hawk, which one associates with brutality and ignorance, has a brain which is but little heavier.

The front part of the organ, known as the cerebral hemispheres, or, more briefly, as the cerebrum, is that part of the brain which is associated with intelligence. Now among the mammals this part of the brain is generally much furrowed, the brain surface being, therefore, increased without any actual increase in the skull-space required. This furrowing is met with in most mammals, but not always in the smaller and in the less intelligent kinds. But in the bird’s brain there are no convolutions: the surface is as smooth as in the reptile. Not even in the artful Raven, which some hold as the most highly developed of birds, is there a trace of the furrowing which one rightly associates, so far as the mammalia are concerned, with a high position in the series. The hinder part of the brain is known as the cerebellum; between this and the cerebrum are the optic lobes, of which there are only two, the mammals having four. From the brain arises the spinal cord, or marrow, which runs in the canal formed by the vertebræ, just as the brain lies in the brain-case. The nerves of the body come off either from the brain or the marrow, but it is not important to enumerate them. They show no difference in different kinds of birds.

The Muscles.

The muscles of a bird are what is popularly known as its flesh. When the skin is removed, the bones are seen to be covered by a mass of this flesh, which is of a red colour, darker in some birds than in others. For instance, in a Duck the colour is a dark red; in a Pigeon, quite a pale brown. The flesh is not, however, merely a thick sheet covering the bones: it can be separated into layers which are themselves made up of a number of separate pieces of muscle. These individual muscles are very commonly of a spindle-like shape, being thickest in the middle and dwindling towards both ends, where they often end in a tough substance called the tendon, which has a glistening and very characteristic appearance. All muscles are not of this form--sometimes they are strap-shaped; and not all of them end in tendons. As the most important act of the bird’s life that depends upon its muscles is flying, it is not surprising to find that the muscle which effects the downward stroke of the wing is the largest. This muscle is known as the great pectoral, and it is said to be almost as large as all the other muscles of the body put together. The way in which a muscle effects the movements of the bones to which it is attached is by contracting. All muscles are able to contract; they shorten, and, accordingly, the ends, with whatever they happen to be attached to are brought closer together. The contraction is governed by the nerves, and it has been discovered that the nerves actually end in communication with the fibres of which the muscle is composed. This pectoral muscle lies on the breast-bone, and nearly completely covers it; indeed, only the edge of the keel appears, and a very little tract at the sides. When this muscle is dissected away another muscle, not nearly so large, comes into view underneath it; this is called the pectoralis secundus, or the second pectoral. Its action is precisely the reverse of that of the great pectoral: it pulls the wing up instead of down. Between them, these two muscles do most of the work in flying. Naturally, in the ostrich tribe, which do not fly, they are much reduced in bulk. But they are never absent altogether, even in the Apteryx, which is, perhaps, further removed from the possibilities of flight than any other bird.

A very curious muscle runs into the patagium of the wing, which is that fold of skin which lies between the shoulder and the hand. This muscle is called the patagial muscle. It starts from the shoulder as a fleshy band, but soon ends in two long tendons: one of these follows the upper margin of the patagium, and finally ends in the wrist; the other passes down over the patagium, and ends below in connection with some of the muscles of the arm, and also by being attached in a fan-shaped way to the skin itself. The function of this muscle is to assist in the folding up of the wing when it is, so to speak, put away after use. The tendons in which the latter part of this muscle ends often show a most complicated branching in the patagium; they frequently offer characteristic differences in different birds, and are made some use of by the systematist. The bird has got a biceps to its arm just as we have. It sometimes happens that this biceps gives off a muscular slip, which runs into the patagium and becomes attached to the upper of the two tendons of the patagial muscle. A good deal of stress is laid by certain ornithologists as to whether this biceps slip is absent or present. Several of the common British birds will afford material to the beginner to ascertain for himself some of the chief variations in these and the other muscles of the body. It will be a good exercise to get a few birds, and to carefully dissect two of them, belonging to as widely different kinds as possible, side by side. You might select, for instance, a Crow and a Pigeon, which are fairly extreme types. To revert to our account of the muscular anatomy of a bird, it will be impossible to attempt any comprehensive account of this branch of the subject, because the facts are so appallingly numerous. We shall content ourselves, therefore, with the mention of a highly characteristic bird muscle which occurs in the leg. This muscle is known as the ambiens. This muscle is thin and ribbon-like. It takes its origin from a little process of the pubic bone usually called the prepubic process. From this point it runs along the inside of the thigh until it reaches the knee; it then bends over the knee and comes out on the other side, where it runs down the leg to join the deep flexor muscle of the foot. When this ambiens muscle contracts it pulls upon the flexor muscle, already referred to; the effect of this is that the toes are brought together by the tendons in which the last-mentioned muscle ends. The ambiens is far from being universally present among birds. It is notably absent from the passerine birds (the Sparrows, Crows, Rooks, and small perching birds generally), and from the Hornbills, Toucans, Woodpeckers, and that varied assemblage known as picarian birds. On the other hand, the Storks, Hawks, and most of the larger birds, have the muscle. But among some of these it is absent; thus, the Owls on the one hand, and the Herons on the other, have no ambiens; but from their general resemblance in other particulars to birds which have an ambiens, it was thought by Professor Garrod that the loss in them was a recent event, and that they might be fairly placed in one great group of birds with an ambiens which he termed, somewhat lengthily, the ‘homalogonatæ,’ or normal-kneed birds, reserving the name ‘anomalogonatæ,’ or abnormal-kneed birds, for the passerines, &c., without an ambiens.

_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.

[Illustration: FIELDFARES. MISSEL-THRUSH. BLACKBIRD.]

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.

* * * * *

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.