by Jay Sharp
The diminutive jerboa looks as though it were made from left-over spare parts of other animals, but it is nevertheless superbly adapted to harsh environments such as those of the Gobi and Sahara deserts. It holds membership in the Dipodinae, or "jumping rodents," family, which includes several different genera. The jerboa belongs to one of three genera that include more than two dozen species, more than 20 of them in Asia.
Characteristics of the Jerboa
Typically, the jerboa has a mouse- or rat-like head and body, cat-like sensory whiskers, owl-like eyes, squirrel-like to jackrabbit-like ears, kangaroo-like back legs, prairie dog-like forelegs and a disproportionally long, sometimes tufted, distinctive tail.
- Size and Weight: Length (head and body), two to six inches, depending on the species; weight, less than an ounce up to a few ounces.
- Head: Skull, shaped much like that of a mouse or rat; nose, strong, adapted for tunneling burrows for refuge; eyes, large, adapted for nocturnal activity; ears, proportionally large to very large, depending on species, and protected by bristly hairs; teeth, curved and grooved chisel-like incisors and strong molars, adapted for eating the tough plant materials of arid lands; sensory whiskers, long and adapted for feeling immediate surroundings in the darkness of night or within burrows.
- Body: Roughly mouse- or rat-shaped, covered with long silky soft fur, generally (depending on the species) buff to dark sandy colored on upper parts, lighter colored under parts.
- Legs and feet: Hind legs, typically four times longer than forelegs, designed for prodigious leaps--up to six to seven feet in height and perhaps ten feet in length; hind feet, large, with central bones fused for added strength and support in leaping; toes, four (Asiatic jerboas) or three (African jerboas); digits and soles, equipped with hair tufts to enhance mobility -- something like snow shoes -- in loose sand; forelegs, small, arm-like with forepaws designed for digging burrows and handling food.
- Tail: Typically longer than head and body, used for support and balance when standing, may be tufted.
- Senses: Keenly developed abilities for smell, hearing and dim-light vision.
Distribution, Habitat and Diet
The jerboa's range extends from Asia west southwestward across northern Africa. It often favors arid sandy habitats such as the Gobi Desert, where temperatures may fall to near zero during the cold of winter, and the Sahara Desert, where temperatures may rise to more than 130 degrees Fahrenheit in the heat of summer. Foraging primarily at night, the jerboa eats plants, seeds and insects, depending on its food to meet its need for water. It may never actually drink free water throughout its life.
A nocturnal animal that spends most of its daylight hours sequestered beneath the surface of the ground, the jerboa has kept much of its behavior secret. It is, however, best known for its leaping ability, which it uses to escape predators. "When about to spring," said the Encyclopedia Britannica, 9th Edition, the jerboa "raises its body by means of the hinder extremities, and supports itself at the same time upon its tail, while the forefeet are so closely pressed to the breast as to be scarcely visible... It then leaps into the air and alights upon its four feet, but instantaneously erecting itself, it makes another spring, and so on in such rapid succession as to appear as if rather flying than running." The jerboa can move 15 to 16 miles per hour. When not in flight, the jerboa walks upright or hops.
Primarily a solitary animal, the jerboa lives alone in its burrow, either in isolation or within a colony. Using its teeth, nose and claws, it may excavate a simple temporary one- to two-foot-long, single-tunnel burrow that is uses for escape from predators or for refuge from extreme temperatures. It also excavates a much more elaborate and more permanent, five- to eight-foot deep burrow that has several tunnels and entrances as well as chambers for hibernation, food storage and nesting. It may line its nesting chamber with shredded vegetation or even camel hair. The jerboa uses plugs of soil to seal entrances, helping to camouflage the burrow, maintain tolerable internal temperatures and contain moisture.
According to the Peoples Trust for the Environment, the jerboa species that live in cold desert environments such as the Gobi hibernate through the winter, living off body fats. The jerboa species that live in the hot desert environments such as the Sahara stay in their burrows, in a state of torpor, through the summers.
The jerboa has also kept its mating and parenting behavior largely secret, but it breeds two or three times each year. The female gives birth to two to six -- typically three -- naked and helpless young, after a relatively long pregnancy. According to authorities D. Eilam and G. Shefer, Department of Zoology, Ramat-Aviv, Israel, a newborn pup's "hindlegs and forelegs are of the same length, the tail is short, skin pigmentation and fur are absent, and the eyes and ears are closed."
Compared with other rodents, the newborn jerboa develops slowly. "...their hind legs do not develop until they are 8 weeks old," according to People's Trust for the Environment. "They cannot jump until they are 11 weeks old. Jerboas are sexually mature at 14 weeks, twice the age at which rats are mature." Once the young jerboa does leave the nest and achieve independence, it may "live in the wild for up to 6 years, twice the life expectancy of rats."
The jerboa appears to face an uncertain future. As it always has, the animal faces a number of predators, especially those that feed at night. These include, for instance, owls, snakes, foxes, jackals and, in populated areas, house cats. The greater long-term threat, however, would seem to be habitat loss, inflicted by man.
A few of the jerboa species -- for instance, the five-toed pygmy jerboa (Cardiocranius paradoxus) and the thick-tailed pygmy jerboa (Salpingotus crassicauda) -- are currently considered as threatened. Other species -- for example, the long-eared jerboa (Euchoreutes naso), of the Gobi Desert, and the well known lesser Egyptian jerboa (Jaculus jaculus), of northern Africa and the Arabian Peninsula -- appear on the International Union for the Conservation of Nature and Natural Resources Red List of Threatened Species, although they are ranked among those of "Least Concern."
Some species, for instance, the long-eared jerboa, have been recommended for more research by international environmental organizations. The jerboa's range, population trends, threats and management requirements need to be better understood if the animal is to be assured of long-term survival.
- With further research, the jerboa's early development may yield new understanding of postnatal "anatomy, histology, physiology, and motor behavior," said Eilam and Shefer.
- Relative to the length of its front legs, the jerboa's back legs are longer than those of the kangaroo, according to the Encyclopedia Britannica, 9th Edition.
- While unrelated, the jerboa, the Australian hopping mouse and the North American kangaroo rat have all developed similar adaptations to sandy, arid environments, providing an example of convergent evolution.
- Extremely shy and elusive, the jerboa evades nearly any attempt at capture. However, said the Encyclopedia Britannica, 9th Edition,"The Arabs...succeed, it is said, in this by closing up all the exits from the burrows with a single exception, by which therefore they are forced to come, and over which a net is placed for their capture."
- It is purportedly the jerboa -- referred to as a mouse -- that finds mention in the Bible, in the book of Leviticus, when the children of Israel are cautioned about they must not eat: "These also shall be unclean to you among the creeping things that creep upon the earth: the weasel, and the mouse, and the tortoise..."
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