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cells or membranous sacs disposed for this purpose over the body: these sacs are situated in the chest, and among the muscles, and between the muscles and the skin; and in some birds are continued down to the wings, and extend even to the pinions, thigh bones, and other parts of the body: for the same purpose the feathers and especially the wing feathers also contain a large quantity of air. Now all these cavities and others not enumerated, such as the hollows of the bones, can be filled and distended with air at the will of the bird: by this means the strength and bulk of the bird is increased, without adding to its weight: and such a general diffusion of air throughout the body must be of infinite service in enabling it to fly, to poise itself in the air, and to skim far above the surface of the earth. Nor is that the only use of this wonderful provision of nature; I again quote Bewick, who says “it is likewise eminently useful in preventing its respiration from being stopped or interrupted by the rapidity of its motion through a resisting medium: were it possible for man to move with the swiftness of the swallow, the actual resistance of the air, as he is not provided with internal reservoirs similar to those of birds, would soon suffocate him.” Another very remarkable peculiarity in the internal economy of birds, is their mode of digestion: the bill, is scarcely if ever, used for mastication, but solely as an instrument of prehension: it is the gizzard whose amazing strength and powers can scarcely be overrated, that grinds down the grain and other food, and renders it fit for digestion. Experiments have been made, by which it has been incontrovertibly proved, that glass, nails, and the hardest substances have in a few hours been filed down by the action of the gizzard, without any injury accruing to it thereby: as a help to this digestive power small stones are often swallowed by birds, which are eminently useful in assisting this grinding process, thus rendering the food more amenable to the gastric juices.
Now after this rapid glance at the general structure of birds, can we conceive anything more adapted for buoyancy and for rapid motion through the air, than their external and internal formation ? We cannot but be struck with their wonderful adaptation to the position which they were created to fill. Let us now push our
enquiries a little farther; and still bearing in mind that they are denizens of the air, and roam at vast distances above our heads, and all around us, examine into the senses and faculties with which they are endowed.
In the first place we shall find them fnrnished with unusual powers of sight, hearing, and smell, and to this end they are supplied with three double organs of sense, viz: eyes, ears, and nasal cavities.
The sight of some, and particularly of the rapacious birds, is so acute and piercing, as to enable them to see their prey from an enormous height in the air, whence they dash down with astonishing swiftness and unerring aim. The vulture sailing in circles at an immense altitude can distinguish his prey on the ground, without the aid of any other faculty than his eyes, as has been clearly proved by experiment: the lordly eagle soaring amid the clouds seems to prefer that elevated station, whence to seek some victim on the earth, and his wonderful power of vision seldom fails to discover the desired object far below: the kestrel hawk, with which all are familiar, balances himself in the air at a considerable height, while his piercing eyes search the ground below for the mice which constitute his food : these are all diurnal birds of prey, and are especially noted for the keenness of their vision: but not less extraordinary is the eye of the owl, which seeks its prey by twilight, and cannot endure the full glare of day: should any accident expose him to the light of the sun, he either closes his eyes entirely, or defends them with a curtain or blind, which is an internal eyelid, and which he can close in an instant. At such times he presents but a grotesque and foolish appearance, but see him as he emerges from his hollow tree, or the ivy clad ruin in the deepening twilight: watch him as he regularly beats the field, and quarters it like a pointer; see him suddenly drop upon the unfortunate mouse that was hurrying through the grass, and judge what acuteness of vision must be there. In the nocturnal species the eyes are usually directed forwards, and are brighter, larger, and clearer than those of the diurnal birds, and thus from their size, position, and construction are admirably calculated for concentrating the dim rays of twilight. In the other Orders we do not expect to find such wonderful powers of sight, for their habits do not require it; yet here too we shall often find considerable quickness and extent of vision. The flycatcher will sit perched on a twig, and suddenly dart upon an insect passing often at a considerable distance, which we are wholly unable to perceive. The bold and sagacious raven and the destructive carrion crow have been famed for their far seeing propensities: the rook too has the same property, for which cause we may constantly see the dull-eyed starlings attaching themselves to their society, and relying on these excellent sentinels, feeding in greater security. The swift careering through the air on rapid wing and dashing past like a meteor, not only can see to steer his way clear of all obstacles, but can discern the passing insect, which it catches in its mouth as it rushes by. The pigeons mounting high into the air, can perceive the grain which they are seeking from an almost incredible distance. The redstart will avoid the shot, by rising on seeing the flash from the cap; and many of the ducks and especially the divers, disappear under water the moment the trigger is pulled, seeing the flash and diving almost instantaneously, and so escaping the death intended for them. These are a few instances of the extraordinary powers of vision belonging to the feathered race. An eminent French naturalist has calculated it to be about nine times more extensive than that of man; and anatomists, after dissecting the eye of the golden eagle, or one of that family, whose sight is considered the keenest of all, declare that nothing can be conceived more perfect than the structure. The eye of the falcon which feeds by day, will differ from that of the owl which feeds by night: both will differ from that of the swan, which has to procure its food under water: but all are exactly adapted to their own peculiar spheres of action, all are capable of very astonishing sight.
Again, the hearing of some is so subtle that they can detect their prey when hidden from view by this sense alone, and by the same power are ever on the alert for the approach of an enemy. As the eagle is the most renowned for powers of vision, so we may without hesitation pronounce the owls to possess a more acute sense of hearing than any other family: it seems that this faculty is given them in common with other nocturnal and crepuscular animals; as, for example the bats, to enable them to guide themselves in their flight on the darkest nights, and to direct them to their prey: the organs with which they are furnished to secure this end are of a very remarkable construction, and developed to an extraordinary extent: the auditory opening, or ear-couch, is sometimes extremely large, and is then furnished with an operculum or cover, which they can open and close at will: but in those species where the aperture is smaller, such an addition is not provided. Another peculiarity in thc nocturnal birds of prey is that the two ears are not alike: the one being so formed as to hear sounds from below, the other from above: this though an old discovery, is not very generally known; though it is doubtless an admirable help to catch the faintest sound proceeding from every direction; and with such organs the owls are enabled to detect in an instant the slightest rustling of their prey. Next to the owl, perhaps the night-jar (or goat-sucker, as it is commonly though erroneously called) possesses the most acute sense of hearing: this bird is also crepuscular, and seldom hunts for moths till the shades of evening; and, as in the owl, its ears are of very large size. But there are many other birds gifted with remarkably acute powers of hearing: see the song-thrush descend on the lawn on a damp morning; watch how he inclines his ear on one side, then hops forwards, and again listens, till at length he draws forth the worm which his fine ear had told him was there, and which alarmed at his hops and peckings had hurried to the surface, supposing they were occasioned by his dreaded enemy, the mole: or visit some fine old heronry, and try to penetrate near their chosen nursery without your presence being detected: these nocturnal birds are not particularly keen of sight during the day, but long ere you can approach them, however cautiously, their keen sense of hearing has told them you are near. Another bird remarkable for possessing this faculty in an eminent degree, is the curlew: of all the shore birds there is not one so difficult of approach as this: his organs of hearing are so sensitive, that it is almost impossible to come near him; and again, the Swedish ornithologist, Professor Nilsson, speaks of the black cock as being most acute both in hearing and in sight. Such are some of the instances one might collect of another sense being possessed by the feathered tribes in extraordinary perfection: that some birds hear more quickly than others is an undisputed fact: but we shall always find, if we examine into it, that to those the most subtle sense of hearing is given, whose habits cause them to require it most; while from those which would not be benefited by it, it is in a measure witheld.
I have spoken of the powers of sight and hearing so conspicuous in birds, I come now to the other sense with which they are provided, that of smell. This too we shall find to be peculiarly delicate in some families, though perhaps generally it is but little required, and therefore but little developed: and we shall for the most part find that those birds whose nostrils are the most conspicuous and open, will possess this sense in the highest degree, while those whose nostrils are concealed and almost impervious will share in it but little. The bird which is certainly most remarkable for this faculty, though of late years it has been gainsayed by certain American naturalists, is the vulture: blessed as I have already remarked, with a keen sense of sight, the vulture soaring through the air, and above the dark forests, is also directed to his prey by the extraordinary perfection of his organs of smell: his food is always putrid, and the effluvium arising therefrom is necessarily most rank: but yet when we read in the accounts of ornithologists, who have seen them in their own tropical countries, the wonderful manner in which these birds will congregate at a putrid carcase, hidden though it may be in a pit or a thick forest, and how first appearing as a speck in the distant heavens, then gradually increasing in size as they come nearer, they arrive singly from all quarters, whereas till then not a single individual was to be seen, we can form some idea of the great powers of smell which these birds must possess. Mr. Waterton who has seen them in Guiana, Demerara, and other parts of Southern America; and Mr. Gosse, who more recently has seen them in the West Indian islands, have published in their respective most interesting little volumes such strong and conclusive evidence of the amazing extent of this sense