The mammalian fauna of most deserts is dominated by small rodents, including
hundreds of species of ground squirrels, mice, rats, kangaroo mice, kangaroo
rats, gerbils, jerboas, and jirds. Their burrowing, nocturnal habits are described
earlier. One of the best-known, from its success as a small, clean, fairly odorfree
pet, is the Mongolian gerbil—technically called the Mongolian jird
(Meriones unguiculatus)—of the Gobi Desert and surrounding regions. This
gerbil exhibits a wide array of adaptations to desert life. It emerges at night to
seek dew-dampened seeds and other plant foods and so never needs to drink. It
may take food back to its burrow to eat it there, out of danger, or to store it for
later. One gerbil is recorded to have hoarded 20 kilograms (44 Ib.) of assorted
seeds in its underground home. Stored seeds in the burrow also act as sponges,
soaking up water from the humid air and moist soil to provide the gerbil with
extra moisture. The bulk of each seed is carbohydrate (plant starch), which
yields metabolic water when digested and broken down inside the body.
The gerbil’ s pa le brown ish u ppe r fur give camouflage on the desert soil,
and the large eyes, big ears, and long whiskers are adapted for night activity. In
common with many other small desert rodents, the large back feet can hop at
speed across soft, open ground. The feet are furry underneath, both to aid grip
and as insulation from the hot sand. The long tail gives balance and works as a
rudder when bounding at speed, and even the gerbil’s underside is white to
reflect heat from the ground below.
In the Atacama and Patagonian deserts of South America the peludos, or hairy
armadillos (genus Chaetophractus), make burrows over 1 meter deep (3 ft.) and
several meters long on the slopes of sand dunes. They are diurnal in winter,
when more than half of their diet consists of plant food. However, they become
more nocturnal in summer to avoid the higher desert temperatures and eat more
small animals such as insects, lizards, snakes, and mice. Like other armadillos,
they are well protected by horny crosswise plates and, when threatened, roll into
a ball. The smallest armadillo species, able to fit on a human palm, is the fairy
armadillo (Clamyphorus truncatus) of Patagonia. Like other armadillos, it is a
powerful digger, with large claws on its strong forelegs. It eats plants, ants,
worms, and snails. However, plowing up the scrubland for farming and attacks
by domestic dogs have gradually reduced its range to the desert regions of west
and central Argentina.