While thus the warmth of summer attracts hosts of migratory birds to the Arctic wildernesses, shoals of salmon and sturgeons enter the rivers in obedience to the instinct that forces them to quit the seas and to swim stream upward, for the purpose of depositing their spawn in the tranquil sweet waters of the stream or lake. About this time also the reindeer leaves the forests to feed on the herbs and lichens of the tundra, and to seek along the shores fanned by the cooled sea-breeze some protection against the attacks of the stinging flies that rise in myriads from the swamps. Thus during several months the tundra presents an animated scene, in which man also plays his part. The birds of the air, the fishes of the water, the beasts of the earth, are all obliged to pay their tribute to his various wants, to appease his hunger, to clothe his body, or to gratify his greed of gain. But as soon as the first frosts of September announce the approach of winter, all animals, with but few exceptions, hasten to leave a region where the sources of life must soon fail. The geese, ducks, and swans return in dense flocks to the south; the strand-birds seek in some lower latitude a softer soil which allows their sharp beak to seize a burrowing prey; the water-fowl forsake the bays and channels that will soon be blocked up with ice; the reindeer once more return to the forest, and in a short time nothing is left that can induce man to prolong his stay in the treeless plain. Soon a thick mantle of snow covers the hardened earth, the frozen lake, the ice-bound river, and conceals them all--seven, eight, nine months long--under its monotonous pall, except where the furious north-east wind sweeps it away and lays bare the naked rock.