Migrations are exchanges for every country (except the poles, at the epoch of winter). The particular condition of climate or food, which decides the departure of one species of birds, is precisely that which determines the arrival of another species. When the swallow quits us at the autumn rains, we note the arrival of the army of plovers and peewits in quest of the lobworms driven from their lurking-places by the floods. In October, and as the cold increases, the greenfinches, the yellow-hammers, the wrens, replace the song-birds which have deserted us. The snipes and partridges descend from their mountains at the moment when the quail and the thrush emigrate towards the south. It is then, too, that the legions of the aquatic species quit the extreme north for those temperate climes where the seas, the lakes, and the pools, do not freeze. The wild geese, the swans, the divers, the ducks, the teal, cleave the air in battle array, and swoop down upon the lakes of Scotland and Hungary, and our marshes of the south. The delicate stork flies southward, when his cousin, the crane, sets out from the north, where his supplies begin to fail him. Passing over our lands, he pays us tribute by delivering us from the last reptiles and batrachians which a warm autumnal breeze has restored to life.
Page [188]. My muse is the light.—And yet the nightingale loses it when he returns to us from Asia. But all true artists require that it should be softly ordered, blended with rays and shadows. Rembrandt in his paintings has exhausted the effects, at once warm and soft, of the science of chiaro-oscuro. The nightingale begins his song when the gloom of evening mingles with the last beams of the sun; and hence it is that we tremble at his voice. Our soul in the misty and uncertain hours of the gloaming regains possession of the inner light.
Page [215]. Do not say, "Winter is on my side."—While M. de Custine was travelling in Russia, he tells us that, at the fair of Nijni-Novgorod, he was frightened by the multitude of blattes which thronged his chamber, with an infectious smell, and which could not be got rid of. Dr. Tschudi, a careful traveller, who has explored Switzerland in its smallest details, assures us that at the breath of the south wind, which melts the snow in twelve hours, innumerable hosts of cockchafers ravage the country. They are not a less terrible scourge than the locusts to the south.
During our Italian tour, my wife and I made an observation which will not have escaped the notice of naturalists; namely, that the cockchafer does not die in autumn. From the inhabited portions of our palazzo, almost entirely shut up in winter, we saw clouds of these insects emerge in the spring, which had slept peacefully in expectation of its warmth. Moreover, in that country, even ephemeral insects do not perish. Gigantic gnats wage war against us every night, demanding our blood with sharp and strident voice.
If, by the side of these proofs of the multiplication of insects, even in temperate or cold countries, we put the fact that the swallow is not satisfied with less than one thousand flies per diem; that a couple of sparrows carry home to their young four thousand three hundred caterpillars or beetles weekly; a tomtit three hundred daily; we see at once the evil and the remedy. We quote these figures from M. Quatrefages (Souvenirs), and from a letter written by Mr. Walter Trevelyan to the editor of "The Birds of Great Britain," translated in the Revue Britannique, July 7, 1850.
I offer the reader a very incomplete summary of the services rendered to us by the birds of our climate.
Many are the assiduous guardians of our herds. The heron garde-bœuf, making use of his bill as a lancet, cuts the flesh of the ox to extract from it a parasitical worm which sucks the blood and life of the animal. The wagtails and the starlings render very similar services to our cattle. The swallows destroy myriads of winged insects which never rest, and which we see dancing in the sun's rays; gnats, midges, flies. The goat-suckers and the martinets, twilight hunters, effect the disappearance of the cockchafers, the gnats, the moths, and a swarm of nibbling insects (rongeurs), which work only by night. The magpie hunts after the insects which, concealed beneath the bark of the tree, live upon its sap. The humming-bird, the fly-catcher, the soui-mangas, in tropical countries, purify the chalice of the flower. The bee-eater, in all lands, carries on a fierce hostility against the wasps which ruin our fruit. The goldfinch, partial to uncultivated soil and the seeds of the thistle, prevents the latter from spreading over the ground. Our garden birds, the chaffinches, blackcaps, blackbirds, tits, strip our fruit-bushes and great trees of the grubs, caterpillars, and beetles, whose ravages would be incalculable. A large number of these insects remain during winter in the egg or the larva, waiting for spring to burst into life; but in this state they are diligently hunted up by the mavis, the wren, the troglodyte. The former turn over the leaves which strew the earth; the latter climb to the loftiest branches, or clear out the trunk. In wet meadows, you may see the crows and storks boring the ground to seize on the white worm (ver blanc) which, for three years before metamorphosing into a cockchafer, gnaws at the roots of our grasses.
Here we pause, not to weary our reader, and yet the list of useful birds is scarcely glanced at.