The strongest instinct of this animal is to clear the ground thoroughly about its burrows; and it is this destructive habit that makes it necessary for cultivators of the soil to destroy all the vizcachas in or near their fields. On the uninhabited pampas, where the long grasses grow, I have often admired the vizcachera; for it is there the centre of a clean space, often of half an acre in extent, on which there is an even close-shaven turf: this clearing is surrounded by the usual rough growth of herbs and giant grasses. In such situations this habit of clearing the ground is eminently advantageous to them, as it affords them a comparatively safe spot to feed and disport themselves on, and over which they can fly to their burrows without meeting any obstruction, on the slightest alarm.
Of course the instinct continues to operate where it is no longer of any advantage. In summer, when the thistles are green, even when growing near the burrows, and the giant thistle (Carduus mariana) springs up most luxuriantly right on the mound, the vizcachas will not touch them, either disliking the strong astringent sap, or repelled by the thorns with which they are armed. As soon as they dry, and the thorns become brittle, they are levelled; afterwards, when the animal begins to drag
304 The Naturalist in La Plata.
them about and cut them up, as his custom is, he accidentally discovers and feasts on the seed: for vizcachas are fond of exercising their teeth on hard substances, such as sticks and bones, just as cats are of "sharpening their claws" on trees.
Another remarkable habit of the vizcacha, that of dragging to and heaping about the mouth of his burrow every stalk he cuts down, and every portable object that by dint of great strength he can carry, has been mentioned by Azara, Darwin, and others. On the level plains it is a useful habit; for as the vizcachas are continually deepening and widening their burrows, the earth thrown out soon covers up these materials, and so assists in raising the mound. On the Buenos-Ayrean pampas numbers of vizcacheras would annually be destroyed by water in the great sudden rainfalls were the mounds loss high. But this is only an advantage when the animals inhabit a perfectly level country subject to flooding rains; for where the surface is unequal they invariably prefer high to low ground to burrow on, and are thus secured from destruction by water; yet the instinct is as strong in such situations as on the level plains. The most that can be said of a habit apparently so obscure in its origin and uses is, that it appears to be part of the instinct of clearing the ground about the village. Every tall stalk the vizcacha cuts down, every portable object he finds, must be removed to make the surface clean and smooth; but while encumbered with it he does not proceed further from his burrows, but invariably re-tires towards them, and so deposits it upon the mound. So well known is this habit, that whatever
Biography of the Vizcacha. 305
article is lost by night--whip, pistol, or knife--;the loser next morning visits the vizcacheras in the vicinity, quite sure of finding it there. People also visit the vizcacheras to pick up sticks for firewood.
The vizcachas are cleanly in their habits; and the fur, though it has a strong earthy smell, is kept exceedingly neat. The hind leg and foot afford a very beautiful instance of adaptation. Propped by the hard curved tail, they sit up erect, and as firmly on the long horny disks on the undersides of the hind legs as a man stands on his feet. Most to be admired, on the middle toe the skin thickens into a round cushion, in which the curved teeth-like bristles are set; nicely graduated in length, so that "each particular hair" may come into contact with the skin when the animal scratches or combs itself. As to the uses of this appendage there can be no difference of opinion, as there is about the serrated claw in birds. It is quite obvious that the animal cannot scratch himself with his hind paw (as all mammals do) without making use of this natural comb. Then the entire foot is modified, so that this comb shall be well protected, and yet not be hindered from performing its office: thus the inner toe is pressed close to the middle one, and so depressed that it comes under the cushion of skin, and cannot possibly get before the bristles, or interfere their coming against the skin in scratching, as certainly be the case if this toe were free as outer one.