BIRDS. THE STRUCTURE AND FOOD OF BIRDS. "Some sought their food among the finny shoals, With slender captives glittering in their beaks; Their eyries inaccessible, and trained Their hardy brood to forage in all weathers."-MONTGOMERY. WE are all fond of birds. We like to mark the sea-gull sitting tranquilly upon the wave that rises and falls beneath. We like to see the sparrow hopping about our doors, and the swallow sweeping in graceful circles to her nest under the eaves of our houses; and we all love to listen to the song of the lark, when, like a speck in the sky, he pours a flood of melody down upon the earth. Birds are very wonderful creatures; but because we see them daily about us we are apt not to think them so. If they were not thus common the case would be very different. Let us suppose that none of us had ever seen a bird, and that a traveller, who had been in distant countries, came home and told us that he had there met with animals that did not swim through the waters like fishes, nor walk on the earth like dogs or horses, but went far higher into the air than a boy's kite, and could move through it at the rate of forty, or sixty, or perhaps, a hundred miles in the hour. How surprised we should all be at this wonderful story! And if we believed that the traveller was telling us the truth, how eagerly would we listen to the description of animals that, instead of being clothed with scales like a fish, or hair like a cow, had the body covered with feathers; and instead of having two fore-legs, like those of our common animals, had the limbs of the fore-part of the body of a different shape, and so contrived, that by their movements the creature was not only sustained in the air, but propelled rapidly forward! If the boys and girls who read this had heard these wonderful facts for the first time, and were talking to each other about these strange unknown animals, all would infer that they must be differently formed from beasts or fishes, and would try to imagine how they were made. Perhaps one might say,-"Their bones must be very strong, for unless they were so, they could not take such long flights." But another might say,-"No; if their bones were very strong, they would be very heavy, and then the bird would not be able to fly at all; the bones, I think, should be very light." Another, who was a little more advanced, might say," It would not be enough that they should be both strong and light at the same time, if that be possible, but the cords or muscles, by which the bones are moved, must be so made as to work with vigour and effect." But then a fourth might exclaim,— "All this would not be sufficient; if I run for a quarter of a mile I am out of breath; how are birds so long-winded, that they can go at so great a rate and for so long a time?” These several points of inquiry can only be answered by the actual examination of the body. It will then be found that the bones do combine the two opposite qualities of lightness and strength. They do so, not only because of the material of which they are composed, but also because of the manner in which they are severally shaped and united together. The muscles, also, will be found to be so formed and so placed that they act with the greatest possible advantage; and with regard to the breathing, an arrangement is made adapted expressly to the wants and habits of birds, and peculiar to them. The air from the wind-pipe passes not only into the lungs, but from them into cavities or air-cells, situated in different parts of the body. The blood is thus more freely exposed to the air than it is in other warm-blooded animals; the body is rendered more light and buoyant, and increased vigour is given to every part of the frame. The air penetrates even into the bones, so that in birds of rapid or powerful flight, the hollow part in the centre of the bone is filled, not with marrow, but with air. If an architect, accustomed, in planning his buildings, to calculate in what way he could shape his timbers so as to combine the greatest lightness with the greatest strength, were to examine the framework of the bones of a bird, he would find all his contrivances there surpassed. If a mechanic were to plan how best the bones might be shaped for certain purposes, and how they could best be moved, he would find his most skilful devices fall far short of the mechanism there exhibited. You all know that the bodies of birds are warm. Their blood is not cold, like that of a frog or a fish; it is not only warm, but is found, in consequence of the way they breathe, to be warmer than that which is in our bodies, or in those of our common domestic animals. This heat would soon pass away from birds as they fly through the air or swim in the water, unless their bodies had some kind of covering to enable them to retain it. A covering has, therefore, been provided for them, which is, at the same time, light and warm. It is, as you well know, formed of feathers; those next the body being shorter and finer, those outside larger, stronger, and tinted with a splendid variety of colours. But this feathery garment would soon be spoiled were no means taken to preserve it: the sun, and the wind, and the rain, would all do it injury, though in different ways. That it may be kept in perfection, it is not only renewed from time to time, but each bird is furnished with a gland, which secretes an oily material fit for the preservation of the feathers. You have seen birds arranging their tost plumage, cleansing off all impurities, smearing the feathers with this oil, and, as you would say, "preening" themselves. You know that if your hands have touched oil or butter, the oiled parts cannot be wet; the oil causes the water to fall off. Now, in those birds that live much upon the water, the oil is very abundant. They smear their feathers with it, the water is repelled, it does not reach their skin, and thus the heat of their bodies is kept up, even when they are for hours in the water. Now, let me suppose I had a very large net—a net like that which you see the fishermen using, but so large that it would extend over a space of two miles on every side-and that I caught at one time all the birds both on sea and land, which the net covered, and brought them here together. Suppose I could collect all the boys and girls who lived in that area, and bring them also here at the same time. If I were then to tell them the different kinds of food these several birds required, I might say to one group of children, "These birds, though differing in size, plumage, and shape of bills, live principally upon fish; I put them under your care: give them their proper food." I might say to others, "These birds feed upon small insects, which live under the bark of trees you will supply them." To others I might say, "These birds with the strong hooked beaks feed upon other birds, and small animals: I put them under your care.' Again, I might desire an assemblage of girls to furnish the seeds, the grains, the worms, and the caterpillars, which form the sustenance of birds of a different kind; or I might place under the charge of a number of boys the members of another family, such as the vulture, whose food should be flesh, and, perhaps, that flesh a little putrid. Suppose you were to exert yourselves ever so much, do you think that you could supply all these several birds with their respective food for a single week? I much doubt if you could; and I am quite sure you would not have all the birds alive at the end of a month. Some would, perhaps, have died from being over-fed, and others of starvation. Yet as it is, week after week, and month after month, all these birds find out for themselves their proper food. We are not aware of the amount of individual exertion it requires. The labour of procuring the food is not obvious. We have to think about it before we rightly estimate its extent. And then we naturally ask ourselves," How are these irrational creatures so wonderfully provided for?” There is but one answer, God feeds them. He teaches to each what is its proper food, and by what means it may be procured; and thus most truly and emphatically may it be said, God feeds them. With this idea many of you are already familiar; for you have read in your Bibles, "Behold the fowls of the air, for they sow not, neither do they reap, nor gather into barns; yet your heavenly Father feedeth them." The Heron. None of the birds that frequent the sea-shore are objects of so much attention as the heron (Ardea cinererea). Every passer-by takes notice of its watchful attitudes, as, standing at the water's edge, it gazes at the flowing tide, or by the margin of one of the little pools upon the shore, waits for its prey, or stealthily approaches its victim. It is most frequently seen near that part of the bay where the banks are oozy, and covered with grass-wrack (Zostera marina). These banks form the sea-meadows, or pasture-grounds of hosts of minute shell-fish and other molluscs; these, again, are preyed upon by fishes of different kinds, and hence these banks form the favourite feeding "ground" of the heron. His fish-dinner can there have its accompaniments of crustacea and mollusca in a state of perfection and freshness that an alderman might envy. Standing singly, or in little groups, along the sea-margin, these birds will remain, as if unconscious of external objects, while the railway trains dash past them laden with passengers. A conviction that the rushing train brought no danger to them seems to have been very quickly arrived at. Occasionally the heron may be seen in a very different situation. There is an extensive wood of dark-foliaged pine and silver fir, mingled with other trees, which crest the upper portion of a high hill within a few minutes' walk of my present residence. This is a favourite resort of the heron. Often have I been struck with the strange appearance of these bulky birds on those trees, where sometimes they assemble in little groups of half a dozen or even more, and I have looked with admiration on the light and peculiar tints of their plumage, contrasted with the foliage. It is worthy of note that herons appear to be more sociable than is generally supposed. The following particulars respecting them have been published by a most accurate observer.1 On the Antrim side of the Bay of Belfast, the herons seldom perch on trees, apparently never, through choice, by day. They "betake themselves singly, or often in little parties of three or four, to the demesnes bordering the estuary, until, in some particular spot, from twenty to perhaps fifty are congregated together. Here they remain in the centre of large pasture-fields or meadows, out of the reach of gun-shot from any fences, until the tide has sufficiently ebbed. A flock of these gigantic birds appears very beautiful when coming silently in view over the banks of fine lofty trees, as I have seen twenty do in a compact body, and not only continue thus in flight, but alight together on the beach." On one occasion (Nov. 1847), forty-two herons were reckoned in a ploughed field from which the sea is not visible. They appeared to great advantage, from their colours contrasting finely with the rich brown hue of the upturned soil. They were mostly at rest, with the necks drawn in, and the plumage puffed out, so as to be apparently of huge bulk. On a sunbright lovely day of November in a different year, the same author, describing the birds observed during a three-mile walk 1 Thompson's Natural History of Ireland, vol. ii. p. 134. |
