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
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.
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