In presenting to the public the second of this series of volumes on Natural History, which treats of the many-voiced and many-coloured tribes that wing their way through the air, it is only necessary to observe, that the Author has pursued the same plan as that which he adopted in treating of the Mammalia. The systematic divisions of modern science are adhered to; and their distinctive characters succinctly, but correctly, and clearly given; while every Family is illustrated by the description, history, and pictorial delineation of one of its constituent species.

These illustrations have again been selected in preference from the Zoology of the British Islands; a course which has been practicable to a much greater extent in the present than in the former volume; for while of the forty-four Families into which the Mammalia are divided, only ​twenty are represented in these islands, of the forty-nine Families of Birds no fewer than thirty-one possess British representatives.

The Author has followed in his arrangement and nomenclature, the "Genera of Birds" of Mr. G. R. Gray; not only on account of the intrinsic authority of that work, but because it is the system on which the noble collection of Birds in the British Museum is arranged and named. The advantage, presented by this volume and its fellows, of being a Manual to the National Collection, will be readily appreciated.

Besides the carefully executed engravings of every species described in the following pages, many others, illustrating peculiarities of structure, &c., are scattered through the book.

London, 1849.

The numerous Class of vertebrated animals which we are about to consider, differs from that of the Mammalia, in that the young are not born alive, but are produced from eggs; which consist of a living point, attached to a globular sac of nutriment, called the yolk, surrounded by a layer of albumen, the glaire, and inclosed in two series of membrane, and a hard calcareous shell. For the development of the vital point into a living and active chick, it is needful that it should receive the stimulus of warmth; and this is, in general, supplied from the body of the parent bird, during the process of brooding or incubation; while it is retained, in most cases, by means of nests, in which the eggs are deposited, and which are composed of substances more or less calculated to resist the rapid abstraction of heat by the surrounding atmosphere. During the process of incubation, which lasts only a few weeks, the yolk is gradually absorbed into the body of the inclosed chick, forming its sustenance, until ​it is ready for exclusion; when, by means of a horny, pointed scale, attached temporarily to the tip of its beak, it succeeds in breaking the eggshell, and forcing its passage into liberty. Some species, as those of the gallinaceous and swimming tribes, are able to run about, and pick up their own food, immediately after their escape from the egg; but more commonly the newly-excluded young are callow and helpless, for several days, unable to quit the nest; and are assiduously fed and tended by the parent birds, with a care which has become proverbial.

In the general structure of their skeleton, Birds agree with Quadrupeds, but in many important particulars it is modified to suit widely different habits, and another sphere of action. Birds are flying animals: their sphere of activity is the air; and their whole organization (we speak not of exceptions) is adapted to a continued suspension in so subtle a medium, and to rapid motion through it. The skeleton unites lightness with firmness; the great bones of the limbs, and many of those of the body, are hollow reservoirs of air communicating with the lungs. Various irregular membranous sacs which can be filled with air, are also distributed about the body; some internally, others between the muscles and the skin, down the throat and chest, or along the tendons of the shoulder: and these communicate with each other, and with the lungs. These ​last named organs are likewise proportionally very large, arranged along on each side of the spine, and occupying the hollows between the bases of the ribs. By this great development of the respiratory system, the blood is more rapidly and effectually oxygenised, and muscular energy greatly increased for the action of flight; while by the animal heat thus evolved the air contained in the complex apparatus described is rarified, and so the body is increased in bulk, but relatively diminished in weight.

The wings of a Bird correspond to the arms and hands of man; but the hand is composed of but two fingers and a thumb, all of which are rudimentary. From the bones of the hand arise the primaries, or quill-feathers properly so called, which are ten in number; these are the largest and strongest feathers of the wing, and the character and power of flight is indicated by their form, stiffness, and relative length. From the principal bone of the fore-arm arise the secondaries, the number of which varies in different species; they are usually shorter, broader, and more flexible than the primaries; and are less removed in form from the general clothing feathers of the body. The bone of the upper-arm (humerus) gives rise to another series of feathers, called tertiaries: these, in some birds, particularly the Plovers, Curlews, &c., are greatly lengthened; they are, however, still weaker in their structure ​than the secondaries. Attached to the little bone which represents the thumb are two or three short and very stiff feathers, called the winglet; they lie upon the basal part of the first primaries at the very edge of the wing. Corresponding to these series of feathers there are, both on the outer and inner surface of the wing, several rows of smaller ones, called coverts, from their office of covering the basal part of the quills.

The feathers of the wing, overlapping each other, present a continuous surface of great breadth, with which the repeated strokes upon the air are performed, which constitute flight. Each feather is concave, whether we regard it transversely or longitudinally; its stem, or midrib, is remarkably strong, though very light, and the beards, which present their edges in the direction of the stroke, are linked to each other by a series of minute hooks. All of these provisions increase the power of the wing in its downward strokes upon the resisting air.

To use these broad fans with sufficient force to impel the bird through the air, large and vigorous muscles are required. Accordingly, in Birds, particularly those of long and powerful flight, the greatest portion of the whole muscular force of the animal is concentrated upon these organs. The muscles which produce the downward stroke of the wing are enormous; and, for their attachment, the breast-bone is not only ​greatly enlarged, but its surface is still further increased by its medial portion rising into a high perpendicular keel or ridge, the two faces of which, from their direction, afford a point of resistance, or purchase, of peculiar advantage.

To resist the tendency of the shoulders to be drawn together by the powerful muscular action exerted during flight, there is inserted between the two bones (coracoids) to which the shoulder-blades are attached, a singular bone of an arched form, well known as the merry-thought. In the common fowl, which flies but little and weakly, this bone is feeble, but in birds of vigorous flight, as the Hawks, the Swallows, and the Humming birds, it is very strong and elastic. On the other hand, where the bird never rises upon the wing, as in the case of the Ostrich, Emu, and kindred birds, this bone is reduced to a mere rudiment.

The posterior extremities also differ materially in structure from those of quadrupeds. The general number of toes is four, which is never exceeded; but a few birds have but three, and the Ostrich but two. For the most part, three toes are directed forwards, and one, answering to the great toe, backwards. The climbing birds, as the Parrots and Woodpeckers, have the outer toe also reversed; while the Swifts have all the four turned forwards. The feet are much more lengthened than in the Mammalia generally, ​especially the tarsal portion, which is never applied to the ground in the action of walking.

Though many birds feed on hard substances, their jaws are entirely destitute of teeth; but are more or less extended into two mandibles, and incased in horny coverings of considerable density, which are exceedingly diversified in form and use. "Thus in birds of prey [the beak] well executes the office of a dissecting knife; in seed-eating birds it forms a pair of seed-crackers for extricating the kernel from the husk which envelopes it; in the Swallows and Goat-suckers it is a fly-trap; in the Swans, Geese, and Ducks, it is a flattened strainer, well furnished with nerves in the inside for the detection of the food remaining after the water is strained, by that particular operation which every one must have observed a common duck perform with its bill in muddy water. In the Storks and Herons we find it a fish-spear; and in the Snipes and their allies it becomes a sensitive probe, admirably adapted for penetrating boggy ground, and giving notice of the presence of the latent worm or animalcule."^[1] The stomach in Birds consists of three parts (which are not, however, in all cases distinctly developed); the crop or craw, the membranous stomach or proventriculus, and the gizzard. The last, which is seen to advantage in the grain-eating birds, is composed of two very ​dense and powerful muscles of a hemispherical form, whose flat faces, coated with a thick skin, work over each other like a pair of millstones, and by the aid of small angular stones, sand, &c., swallowed for the purpose, grind down the hardest substances in a very short time.

With the exception of the beak and the hinder extremities, every part of a Bird is, for the most part, clothed with feathers. The feet are protected by a naked, scaly skin, which in some species extends partly up the leg (tibia). The soles of the toes are covered with a callous modification of this skin, having a granular surface. The plumage of Birds attracts universal admiration, for its beautiful fitness for the ends it answers, for its softness, its smoothness, its compactness, and for its ever varied hues. The most brilliant colours in nature are lavished upon the feathers of these tenants of the sky; embellished and set off in some instances with a peculiar reflection that rivals the lustre of burnished metals, or the radiance of precious stones.

Every one is familiar with the general form of a feather. "When a bird has just left the egg, its covering is a downy kind of hair, several little bundles taking their rise from one common bulb. This is the origin of the future feather. A dark cylinder soon makes its appearance, from the upper extremity of which the sprouting feather emerges, while the lower extremity receives the ​blood-vessels which supply the vascular nourishing pulp of the barrel. When this pulp has performed its office, and the stalk and other parts of the feather are fully developed, it shrivels up into the well-known substance, which every one finds in a quill when he cuts it for the purpose of making a pen."^[1]

As in the Mammalia, the classification of Birds into Orders is founded upon the organs connected with motion and food; that is to say, the characters are taken principally from the beak and feet. The subordinate divisions depend chiefly upon the form of the beak, and pass into each other by almost imperceptible gradations, insomuch that there is no other class of animals in which the genera and sub-genera are so little susceptible of definite limitation.

In the present work we shall adopt the Orders enumerated in the "List of the Genera of Birds" of Mr. G. R. Gray, which are eight in number, viz., Accipitres, Passeres, Scansores, Columbæ, Gallinæ, Struthiones, Grallæ, and Anseres.