Gerbils are ratlike rodents in the mammalian family Muridae, which also includes rats, mice, voles and lemmings. Some authorities place the gerbils in a separate family Gerbilidae, together with the pigmy gerbils. Wild gerbils are rat-sized, long-tailed rodents with rather long hind feet. Nearly all live in self-dug burrows and forage at night feeding mostly on seeds.
Gerbils are probably derived from hamsterlike rodents, and fossil gerbils have been consistently found since the Upper Miocene. Gerbils are found in desert and semi-desert areas of Africa, Mongolia, southern Siberia, northern China, Sinkiang, and Manchuria. There are at least 70 species of true gerbils. Members of the genus Gerbillus have yellow to light grayish brown long and delicate hair, which is snow-white on the belly. They appear delicate and ghostlike, with big dark eyes. Gerbillus campestris is common in northern Africa, and is known for the absence of hair on the soles of the hind feet. Gerbillus gerbillus is a small gerbil found mostly in sandy desert in Egypt, and has no hair on its soles. The Namib gerbil of the genus Gerbillurus found in the Kalahari region is known to survive without drinking water.
The naked-soled gerbils of the genus Tatera, look very much like rats in shape and size and populate somewhat wetter habitats than do other species of gerbils. The naked-soled gerbils are found from Syria to India and Sri Lanka in Steppes and semi-deserts. Tatera robusta lives in Africa, from the Sahel region through eastern Africa to Tanzania.
In the United States gerbils are popular pets and are valuable as laboratory animals for scientific research. This gerbil is also known as the jird, and its taxonomic name is Meriones unguiculatus. This species is somewhat different from true gerbils of the genus Gerbillus. Meriones unguiculatus was brought to the United States in the early 1950s from Mongolia for laboratory research and is often referred to as the Mongolian gerbil. They are highly adaptable and there is danger that they may become established in the wild if released.
The natural habitat of the Mongolian gerbil is desert or semi-desert from the Sahara to the Gobi Desert. Jirds are usually sand-colored and have tails about as long as the body. The molar teeth have a chewing surface that resembles that of burrowing mice with high crowns and small roots. The ears of the Mongolian gerbil are relatively short and their hind feet make them appear sturdier than other gerbils. They are primarily active during the night and their diet includes leaves, seeds, and insects. They live in small colonies and, when upset, they may drum with their hind feet like rabbits. Like other gerbils, jirds have a sebaceous gland in the center of the belly. They smear the secretion on various objects to mark their territories, and recognize each other by scent.
There is no evidence of hibernation or aestivation, and the Mongolian gerbil may be active throughout the year, either by night or day. This species adapts to a range of temperatures from sub-zero to above 86°F (30° C). It may remain underground for long periods depending on the amount of stored food. Daily summer movements of the Mongolian gerbil may cover 0.75-1.1 mi (1.2-1.8 km). One marked animal moved as far as 31 mi (50 km). Its social behavior under laboratory conditions indicates that adults may live together, but the introduction of a stranger may result in a fight to the death. Females are as territorial and aggressive as the males. Some studies suggest that males disrupt maternal behavior and many young are lost. But monogamous pairs seem to do well and some males share in caring for the young, cleaning, grooming and warming the newborns. Fathers and juvenile males help to rear the younger animals.
Wild Mongolian gerbils breed from February to October and up to three litters may be produced each
year. Captive gerbils may breed all year round. The estrous cycle lasts four to six days and may occur right after the birth. Gestation lasts 19-21 days although longer periods of 24-30 days were reported. There are usually 4-7 young born, but litter sizes vary from 1-12. Newborn gerbils weigh about 0.09 oz (2.5 g). They open their eyes after 16-20 days, and are weaned between 20 and 30 days. Gerbils reach sexual maturity in 65-85 days and females may reproduce for 20 months, although in the wild they may not survive for more than three or four months.
Mongolian gerbils kept as pets should be provided with a clean, comfortable, escape-proof cage. They must be protected from cats and from rough handling. With gentle and loving care they become quite tame and respond to the keeper. It is usually best to separate pregnant females so that birth occurs without the interference of other adults, especially the males, although males occasionally care for newborns. Picking up and handling newborns should be avoided because the mother may become excited and kill them. A good healthy diet must include some fresh greens and sufficient protein from a good standard gerbil diet.
See also Hamsters.
Barrie, Anmarie. The Proper Care of Gerbils. Neptune City, NJ: TFH Pubs, 1992.