The common name for more than 100 species of small rodents making up the subfamily Gerbillinae in the family Muridae. Gerbils inhabit the desert regions, steppes, and sandy wastes of Asia, Africa, and southern Russia, often living many miles from water. There are approximately 16 genera of gerbils, including Gerbillus, Gerbillurus, Meriones, Pachyuromys, Psammomys, Tatera, and Taterillus. See also: Rodentia
Most gerbils (see illustration) are about the size of a rat and are protectively colored to resemble the desert sands in which they live. On average, they have a head and body length of 50–200 mm (2–8 in.), a tail length of 56–245 mm (2.24–9.8 in.), and a weight of 10–227 g (0.35–7.95 oz). Gerbils have large ears, large hind feet, well-developed claws, and a long tail. Some have hair on the soles of the feet and bristles on the toes, presumably to prevent them from sinking into loose soil. The smallest is the Brauer's pouched gerbil (Desmodilliscus braueri), with a head and body length of 41–74 mm (1.64–2.96 in.), a tail length of 33–49 mm (1.3–1.96 in.), and a weight of 6–14 g (0.21–0.49 oz). The fat-tailed gerbil (Pachyuromys duprasi) has a tail that is half as long as its body. The tail is thickened and sausage-shaped, and serves as a fat-storage organ for this species, which does not store food in its burrows.
Many small mammals (for example, gerbils, kangaroo rats, jerboas, golden hamsters, and elephant shrews) living in hot, arid conditions have relatively large auditory bullae (the bulbous bones enclosing the hearing apparatus). The arid air of the desert has poor sound-carrying qualities in comparison to cooler, more humid air. Thus, the external ears are large and very sensitive, and are said to be suitable for receiving long-range, low-frequency sounds. The inflated bullae increase the volume of the air-filled chambers surrounding the middle ear, which in turn reduces the resistance to the inward movement of the tympanic membrane. The malleus, part of which is greatly lengthened, is allowed to rotate more freely and has increased leverage. This transforms relatively weak vibrations of the greatly enlarged tympanic membrane into more powerful movements that are transmitted to the incus and the small footplate of the stapes, which rests against the oval window of the inner ear. See also: Ear (vertebrate); Hearing (vertebrate)
Gerbils display varying degrees of saltatory (jumping) locomotion. They are often called antelope rats because of the way in which they move about. They hop rather than scamper or scurry in typical rat fashion. In this respect, they are similar to jerboas, or jumping rodents; indeed, “gerbil” is just another form of the name “jerboa.” See also: Jerboa
Habitat and behavior
Gerbils are primarily nocturnal mammals. They are active year-round, although their activity may be reduced during the winter in some areas. They feed on seeds, grasses, and roots, which for the most part contain a little moisture. Food may be stored for winter use. Some species may also include insects, birds, and bird eggs in their diet.
Fat sand rats (Psammomys) [see illustration] have the most efficient kidneys known; however, the necessity for efficiency is not a lack of water, but an abundance of salt. Sand rats are desert rodents, but their habitat is restricted to the edges of saline and brackish waters. Sand rats feed on plants containing 80–90% water with about twice the salinity of seawater. The plentiful salt content makes it necessary for the sand rat's kidneys to be able to greatly concentrate the urine. See also: Excretion; Kidney
Gerbils live in burrows excavated in the sand. These burrows are variable in structure and may contain several levels, with nest chambers, lengthy tunnels, and food storage chambers. Gerbils may be sociable, sharing community tunnels, or they may lead a solitary life. Males and females usually do not nest together. See also: Burrowing animals
The largest of the gerbils are the great gerbil and the large naked-soled gerbils. The great gerbil (Rhombomys opimus) lives in central Asia from the Caspian Sea to southern Mongolia and north-central China, Iran, Afghanistan, and western Pakistan. Adults have a head and body length of 150–200 mm (6–8 in.) and a tail length of 130–160 mm (5.2–6.4 in.). The fur is thick and soft, and the tail is hairy, almost bushy. The soles of the feet are hairy, and the toes end in large claws. Females are polyestrous and produce two or three litters annually. Litter size may range from 1 to 14, and the young are born after a gestation of 23–32 days. Females may reach sexual maturity at 3–4 months. Longevity ranges from 2 to 4 years. This species is considered a pest in central Asia, where it damages crops, railway embankments, and irrigation channels. It is also a reservoir for plague. See also: Plague
The large naked-soled gerbils (Tatera) have a head and body length of 90–200 mm (3.6–8 in.), a tail length of 115–245 mm (4.6–9.8 in.), and a weight of 30–227 g (1–8 oz). The body is heavy and ratlike. The dorsal coloration ranges from grayish to brownish; the underparts are white or whitish. The soles of the feet are naked. These gerbils usually walk on all four limbs. When alarmed, they escape by bounding as high as 1.5 m (4.9 ft). One species is said to be able to cover 3.5 m (11.5 ft) in one leap.
The Mongolian gerbil or jird (Meriones unguiculatus) has become the most widely known species of gerbil because it has become a laboratory and pet animal and is commercially traded almost worldwide. This species is gregarious and makes a good pet in captivity.