The Ground Squirrels differ from the true squirrels in several respects, though the chief difference lies in the fact that the former make their nest or lair upon the ground, while the latter universally lodge themselves aloft among the branches. The Ground Squirrels can climb, and appear to ascend trees almost as nimbly as their congeners; but they rarely do so unless when pursued, and then but seldom go beyond the lower forks or branches. Their nest is usually in some hole or cavity among the roots, though several species have been lately discovered in rocky regions, dwelling in the crevices of rocks. They approach in habits to the marmot tribe, and seem to link the tree squirrels with these last. Usually, these ground squirrels are striped longitudinally with black, red, and white stripes, giving them a fine appearance; and the species are of different dimensions, from that of the ordinary squirrel to the size of a mouse. In America, for a long time, but one kind was supposed to exist; but latterly a great number of species have been observed and described: denizens of the far West—of the prairies, and remote valleys of the Rocky Mountains.
The African species of ground squirrel, already mentioned as the Palm Squirrel, has its dwelling among the palm trees, on the fruit and roots of which—especially that of the date-palm—it subsists. It is also an inhabitant of India, where there is at least one other species of palm ground squirrel.
In Europe, and throughout the whole of Northern Asia, the ground squirrels are represented by the burunduk—a very interesting little species, quite similar in habits to those of North America.
The Flying Squirrels are the last of the group. These are the most singular of all, and resemble great bats more than squirrels. They possess the power, not exactly of flight, but of making very long leaps from a higher to a lower level, so long that they might almost be regarded as flights. They can pass from one tree to another standing more than a hundred yards apart, and this without descending more than a few feet below the level from which they started. This feat they are enabled to perform by means of a broad membrane that extends from the skin of their fore-legs to that of their thighs, and which, when stretched out, endows them with the properties of a parachute. Their bodies, too, have a flattened shape like the bats; and this also helps to sustain them in the air.
They are true squirrels, however, living upon trees, as the common squirrels do, and looking very like the latter, notwithstanding their winged legs. In one point, however, they differ essentially from the common squirrels; and that is, they are nocturnal in their habits. In the daytime they are never seen, except by accident; but in the twilight, and during a clear night, they may be observed making their long leaps from tree to tree, through the glades or along the edges of the forest. There are several species inhabiting the forests of America, and of late California has yielded several new ones. In the tropical forests of America there are several large species, and the Old World has its flying squirrel in the Polatouka, which inhabits the pine forests of Northern Europe and Asia.
The largest species of these singular quadrupeds appears to belong to the Oriental Islands—to Java, Sumatra, the Philippines, and Moluccas, or Spice Islands, as also to Japan. The great Teguan, or flying squirrel of the Moluccas, is in reality as large as a cat!
The singular Ay-ay of Madagascar is sometimes classed among the squirrels and sometimes among the lemurs. It certainly bears a great resemblance to the squirrel family; but the habits of all animals belonging to Madagascar are so little known that it is difficult to assign them to that exact genus in which Nature intended they should be placed.