921. BIRDS ARE DISTRIBUTED OVER EVERY PART OF THE GLOBE, being found in the coldest as well as the hottest regions, although some species are restricted to particular countries, whilst others are widely dispersed. At certain seasons of the year, many of them change their abodes, and migrate to climates better adapted to their temperaments or modes of life, for a time, than those which they leave. Many of the birds of Britain, directed by an unerring instinct, take their departure from the island before the commencement of winter, and proceed to the more congenial warmth of Africa, to return with the next spring. The causes assigned by naturalists for this peculiarity are, either a deficiency of food, or the want of a secure asylum for the incubation and nourishment of their young. Their migrations are generally performed in large companies, and, in the day, they follow a leader, which is occasionally changed. During the night, many of the tribes send forth a continual cry, to keep themselves together; although one would think that the noise which must accompany their flight would be sufficient for that purpose. The flight of birds across the Mediterranean was noticed three thousand years ago, as we find it said in the book of Numbers, in the Scriptures, that "There went forth a wind from the Lord, and brought quails from the sea, and let them fall upon the camp, and a day's journey round about it, to the height of two cubits above the earth."
922. IF THE BEAUTY OF BIRDS were not a recommendation to their being universally admired, their general liveliness, gaiety, and song would endear them to mankind. It appears, however, from accurate observations founded upon experiment, that the notes peculiar to different kinds of birds are altogether acquired, and that they are not innate, any more than language is to man. The attempt of a nestling bird to sing has been compared to the endeavour of a child to talk. The first attempts do not seem to possess the slightest rudiments of the future song; but, as the bird grows older and becomes stronger, it is easily perceived to be aiming at acquiring the art of giving utterance to song. Whilst the scholar is thus endeavouring to form his notes, when he is once sure of a passage, he usually raises his tone, but drops it again when he finds himself unequal to the voluntary task he has undertaken. "Many well-authenticated facts," says an ingenious writer, "seem decisively to prove that birds have no innate notes, but that, like mankind, the language of those to whose care they have been committed at their birth, will be their language in after-life." It would appear, however, somewhat unaccountable why, in a wild state, they adhere so steadily to the song of their own species only, when the notes of so many others are to be heard around them. This is said to arise from the attention paid by the nestling bird to the instructions of its own parent only, generally disregarding the notes of all the rest. Persons; however, who have an accurate ear, and who have given their attention to the songs of birds, can frequently distinguish some which have their notes mixed with those of another species; but this is in general so trifling, that it can hardly be considered as more than the mere varieties of provincial dialects.
923. IN REFERENCE TO THE FOOD OF BIRDS, we find that it varies, as it does in quadrupeds, according to the species. Some are altogether carnivorous; others, as so many of the web-footed tribes, subsist on fish; others, again, on insects and worms; and others on grain and fruit. The extraordinary powers of the gizzard of the granivorous tribes, in comminuting their food so as to prepare it for digestion, would, were they not supported by incontrovertible facts founded on experiment, appear to exceed all credibility. Tin tubes, full of grain, have been forced into the stomachs of turkeys, and in twenty-four hours have been found broken, compressed, and distorted into every shape. Twelve small lancets, very sharp both at the point and edges, have been fixed in a ball of lead, covered with a case of paper, and given to a turkey-cock, and left in its stomach for eight hours. After that time the stomach was opened, when nothing appeared except the naked ball. The twelve lancets were broken to pieces, whilst the stomach remained perfectly sound and entire. From these facts, it is concluded that the stones, so frequently found in the stomachs of the feathered tribes, are highly useful in assisting the gastric juices to grind down the grain and other hard substances which constitute their food. The stones, themselves, being also ground down and separated by the powerful action of the gizzard, are mixed with the food, and, no doubt, contribute very greatly to the health, as well as to the nourishment of the animals.
924. ALL BIRDS BEING OVIPAROUS, the eggs which they produce after the process of incubation, or sitting for a certain length of time, are, in the various species, different both in figure and colour, as well as in point of number. They contain the elements of the future young, for the perfecting of which in the incubation a bubble of air is always placed at the large end, between the shell and the inside skin. It is supposed that from the heat communicated by the sitting bird to this confined air, its spring is increased beyond its natural tenor, and, at the same time, its parts are put into motion by the gentle rarefaction. By this means, pressure and motion are communicated to the parts of the egg, which, in some inscrutable way, gradually promote the formation and growth of the young, till the time comes for its escaping from the shell. To preserve an egg perfectly fresh, and even fit for incubation, for 5 or 6 months after it has been laid, Réaumur, the French naturalist, has shown that it is only necessary to stop up its pores with a slight coating of varnish or mutton-suet.
925. BIRDS HOWEVER, DO NOT LAY EGGS before they have some place to put them; accordingly, they construct nests for themselves with astonishing art. As builders, they exhibit a degree of architectural skill, niceness, and propriety, that would seem even to mock the imitative talents of man, however greatly these are marked by his own high intelligence and ingenuity.
"Each circumstance
Most artfully contrived to favour warmth.
Here read the reason of the vaulted roof;
How Providence compensates, ever kind,
The enormous disproportion that subsists
Between the mother and the numerous brood
Which her small bulk must quicken into life."
In building their nests, the male and female generally assist each other, and they contrive to make the outside of their tenement bear as great a resemblance as possible to the surrounding foliage or branches; so that it cannot very easily be discovered even by those who are in search of it. This art of nidification is one of the most wonderful contrivances which the wide field of Nature can show, and which, of itself, ought to be sufficient to compel mankind to the belief, that they and every other part of the creation, are constantly under the protecting power of a superintending Being, whose benign dispensations seem as exhaustless as they are unlimited.
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