The Voyage of the Beagle - The Original Classic Edition. Darwin Charles

It is a singular fact, that although the Agouti is not now found as far south as Port St. Julian, yet that Captain Wood, in his voyage

       in 1670, talks of them as being numerous there. What cause can have altered, in a wide, uninhabited, and rarely-visited country, the

       range of an animal like this? It appears also, from the number shot

       by Captain Wood in one day at Port Desire, that they must have been considerably more abundant there formerly than at present. Where the Bizcacha lives and makes its burrows, the Agouti uses them; but where, as at Bahia Blanca, the Bizcacha is not found, the Agouti burrows for itself. The same thing occurs with the little owl of

       the Pampas (Athene cunicularia), which has so often been described

       as standing like a sentinel at the mouth of the burrows; for in Banda Oriental, owing to the absence of the Bizcacha, it is obliged to hollow out its own habitation.

       The next morning, as we approached the Rio Colorado, the appearance

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       of the country changed; we soon came on a plain covered with turf,

       which, from its flowers, tall clover, and little owls, resembled

       the Pampas. We passed also a muddy swamp of considerable extent, which in summer dries, and becomes incrusted with various salts; and hence is called a salitral. It was covered by low succulent

       plants, of the same kind with those growing on the sea-shore. The

       Colorado, at the pass where we crossed it, is only about sixty yards wide; generally it must be nearly double that width. Its course is very tortuous, being marked by willow-trees and beds of reeds: in a direct line the distance to the mouth of the river is

       said to be nine leagues, but by water twenty-five. We were delayed crossing in the canoe by some immense troops of mares, which were swimming the river in order to follow a division of troops into the interior. A more ludicrous spectacle I never beheld than the

       hundreds and hundreds of heads, all directed one way, with pointed ears and distended snorting nostrils, appearing just above the

       water like a great shoal of some amphibious animal. Mare's flesh is

       the only food which the soldiers have when on an expedition. This gives them a great facility of movement; for the distance to which horses can be driven over these plains is quite surprising: I have been assured that an unloaded horse can travel a hundred miles a day for many days successively.