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limited. Such birds are seldom so denuded of feathers as to be unfit for pretty vigorous flight. Birds which migrate from region to region moult more periodically; and in places where the migration is extensive, it will perhaps be found, upon further examination, that the bird moults twice in a year, though in most instances the spring moult is less general than the autumnal one, being in many birds, the males especially, rather a change of colour than of all the feathers. Birds which migrate polarly, or for the purpose of breeding, generally receive their nuptial colours, if not their plumage, after they arrive; but when they migrate equatorially, they change their plumage before they begin their journey. The vernal change in the plumage of birds is owing to the same cause as the change of their voices, from the chirp or cry to song; and in a state of nature the two cease together."
Migration Of Birds.
Birds, generally speaking, says Cuvier, appear to belong more to the air than to the earth. They constitute moving republics, which traverse the atmosphere at stated periods, in large bodies. These bodies perform their aerial evolutions like an army, crowd into close column, form into triangle, extend in line of battle, or disperse in light squadrons. The earth and its climates have less influence on them than on quadrupeds, because they almost always live in similar degrees of temperature, passing the winter in hot climates, and the summer in cold. The continual interchange of birds establishes a communication between all countries, and keeps up a sort of equilibrium of life. The bird passing in summer from the equinoctial climates to the cold regions of the north, and again in winter from the poles towards the equator, knows, by an admirable instinct, the winds and the weather which are favourable to his voyage. He can long foresee the approach of frost, or the return of spring, and learns the science of meteorology from the element in which he almost constantly lives. He needs no compass to direct his course through the empire of the clouds, the thunder, and the tempest; and while man and beast are creeping on the earth, he breathes the pure air of heaven, and soars MIGEATION OF BIEDS.
upwards nearer to the spring of day. He arrives at the term of his voyage, and touches the hospitable land of his destination. He finds there his subsistence prepared by the hand of Providence, and a safe asylum in the grove, the forest, or the mountain, where he revisits the habitations he had tenanted before, the scene of his former delights, the cradle of his infancy. The stork resumes his ancient tower, the nightingale the solitary thicket, the swallow his old window, and the redbreast the mossy trunk of the same oak in which he formerly nestled. All the volatile species which disappear in the winter do not, therefore, change their climate. Some retire into remote places, to some desert cave, some savage rock, or ancient forest, from whence they sally at the close of winter, and spread themselves through the country.
Other families of birds do not, properly speaking, emigrate. They content themselves with approaching the southern climates, in proportion as they are pursued by the cold. The species called erratic, such as the greenfinches of the Ardennes, larks, ortolans, other frugivorous races, and especially parrots, go in troops begging, as it were, their subsistence on the passage. Others follow the track of cultivation, and spread themselves in proportion with the habitations of men.
Of the birds which migrate every year, some depart in autumn and return in spring, while others depart in spring and return in autumn. Our insectivorous races, and many granivorous, finding nothing at the beginning of winter but a soil deprived of its productions, presenting everywhere the image of desolation and death, are necessitated to betake themselves to more favoured climes. Those which, through negligence or weakness, remain behind, drag out a miserable existence, and constantly perish from famine in the midst of frost and snow.*
As our summer birds abandon us towards the close of autumn, we receive, at the same time, fresh supplies of feathered hordes from the populous north. When the weather grows dull, we see passing through the misty
* How truly do these wretched little birds verify the old proverb that "God takes care of those who take care of themselves."—Ed.
air large detachments of woodcocks, of lapwings, and of plovers: these are followed by triangular bands of cranes, storks, of teal, of wild geese, and ducks. They delight in inundated fields, or reedy marshes, or spread themselves in the glades of humid and denuded woods. They continually utter clamorous and melancholy cries, in accordance with the bleak and wintry scene around them. It is a most curious circumstance to observe that the cranes leave and return every year, with marvellous exactness, on the same days.
The Palmipedes and Gralhe come to us every winter from the northern climates, whither they are driven by the ice, and return in spring to their cold and humid habitations. The insectivorous and granivorous races return with the flowers and fine weather, from southern regions, to their native country, allured by the expectation of renewed enjoyment and abundant food. It is at the periods of the equinoxes that these great voyages of birds are performed. These are also the periods of great winds, as if nature had intended that the birds should be thus assisted in their flight. The cold which drives the birds of the polar regions into more temperate climates, sends those of temperate climates into the hot countries. But on the first indication of summer the hot climates send back to the temperate their aerial inhabitants, and the temperate send back to the cold regions their native tribes. Thus there is a general concentration of birds towards the torrid zone in winter, and a general dispersion towards the poles in summer.
The triangular figure which migrating birds adopt in their flight is the most favourable for cutting the air. The bird placed at the point is the most fatigued of the entire band; accordingly each takes this place in turn. The migrations of fishes are conducted in the same manner: the most robust places himself at the head; the other males follow, and the females and young come last. When the ranks of the storks are broken by the wind, they condense into a circle; they do the same when attacked by an eagle. Thus it appears that whatever the migrations of birds may be, yet do they all adopt a peculiar country—each species has its distinct and never-varying habitat, where at a particular period of the year it may certainly be found. In the study of the
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natural history of the feathered tribes, it is of great importance to remember this fact, and to note with exactness the times and seasons of departure and return. Nothing is more remarkable, nothing more truly wonderful in nature, than the regularity and celerity of these annual migrations; the immense extent of illimitable space which the birds traverse, guided only by an unerring instinct; the intuitive knowledge which they seem to possess of the very day and hour of departure; the common consent with which they act, and the certain appointed order which they appear to preserve in their flight, all are evidences that a higher wisdom than mere animal intelligence, or than even human reason, must direct their motions.
"Other facts deserve attention," writes Bishop Stanley, in his valuable work on birds, "proving that mere climate is by no means, in all cases, the cause of these periodical visits. Thus, some birds will, on the introduction of a new system of cultivation, make their appearance in countries where they were never seen before. The crossbill (Loxia curvirostra) has followed the apple to England. Glenco, in the Highlands of Scotland, never saw the partridge till its farmers of late years introduced corn into their lands. The sparrow again extended its range with the tillage of the soil. Thus, during the last century, it has spread gradually over Asiatic .Russia, towards the north and east, always following the progress of cultivation. The foregoing instances, while they assure us (if assurance were necessary) that birds at wonted times change their habitations, still add to, rather than remove, the difficulties as to the real causes. But of these we must for the present remain in ignorance, we have enough left in the actual facts of migration to call forth all our wonder, in considering the regularity, order, and discipline, with which these unaccountable journeys are conducted; and the unknown compass, placed within the bosoms of these airy travellers, enabling them to go and return from points thousands of miles apart, with as much certainty as the sailor steers his ship across the ocean by his skill in navigation, and that mysterious needle ever pointing to the north.
"It is indeed the instinctive power and stimulus which is the real point to excite our astonishment in the migration of birds; for when we take into consideration what has been said of their rapid flight, which would enable an eagle in nine days, allowing him sixteen or seventeen hours for repose, to go round the world, there is nothing so very extraordinary in the journey of a swallow from the shores of England to those of Sierra Leone in Africa.
"Birds, too, in their longer flights, no doubt avail themselves of different currents in the air; for we know that often, when the lower stream of air is blowing from the west, another stream far above may be blowing from another direction: this may be frequently seen by the motion of the upper clouds moving in contrary directions from those at a lower level.
"One other very remarkable fact connected with these long journeys, undertaken by birds over seas and lands, is that they are gifted with some secret power, enabling them not only to find their way to and from the distant countries they visit, but actually guiding them to the very same place from whence they came, and the very same spots for building their nests. This has been done by marking the claws of swallows which were in the habit of building in sheds or outhouses, where they could easily be retaken on their return in the spring and examined.
"It has been observed, that the time of departure of certain birds is by no means so exact as that of their arrival, which may be accounted for by a natural disinclination on the part of the old ones to desert the nests of young ones still requiring their care. But even this most powerful of all instincts, the attachment of a parent to its young, is not in all cases strong enough to conquer the still stronger impulse for migration; for swallows will actually desert their nests, and leave helpless little ones to perish by hunger, rather than remain long after their companions. A pair of martins, which had deserted their family in the autumn, on returning in the spring, were observed to drag out the bodies, which had most probably formed a dried mass with the wool and feathers in the interior, they entirely closed up the opening of the nest with clay, and leaving them thus entangled, proceeded to build another nursery."