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RODENTIA; MURIDAE; Genus PSAMMOMYS
Cretzschmar, 1828

Fat Sand Rats

There are two species (Cockrum, Vaughan, and Vaughan 1977; Corbet 1978; F. Petter, in Meester and Setzer 1977):
Head and body length is 130-85 mm and tail length is 110-50 mm. The upper parts are reddish brown, reddish, yellowish, or sandy buff, and the underparts are yellowish, buffy, or whitish. The tail is fully haired and has a terminal tuft. The external form is stocky. From Meriones, this genus is distinguished by its nongrooved incisors and short (10-15 mm), thick, rounded ears.
Fat sand rats are mainly diurnal and live in sandy areas with scant vegetation. They construct complex burrows with several entrances and food storage chambers and a chamber containing a nest of finely cut vegetation. They sit up on their hind legs and tail but quickly retreat into their burrows when alarmed. Studies in the Sahara Desert (Daly 1979; Daly and Daly 1973) have shown that the preferred food of fat sand rats is the leaves and stems of succulent plants of the family Chenopodiaceae, which contain much water but also a high proportion of salt. Most mammals could not survive by eating these plants without also having an abundant source of fresh water, but fat sand rats thrive on this diet through the aid of their extremely powerful kidneys, which produce a urine with a high salt concentration. Psammomys also feeds on other kinds of plants and reportedly can be very destructive to grain; 500 heads of barley were once found stored in a burrow (Harrison 1972).
During a five-month study of fat sand rats in the Algerian Sahara, Daly and Daly (1975b) calculated average home range length to be 189.6 meters in males and 75.8 meters in females. Mean weekly range lengths were 67.7 meters in males and 11.7 meters in females. Females tended to remain in small areas around the bushes they used for food and to move only when edible vegetation was exhausted. Subordinate males also used a small home range but moved more frequently. Dominant males ranged over relatively large areas encompassing the ranges of several females and subordinate males. A conspicuous form of communication observed in this study was audible footdrumming, sometimes accompanied by a high-pitched squeak. Throughout this study, which lasted from December to April, females were pregnant, lactating, or both; and local people said that young could be found in any month of the year. Associated laboratory work indicated that the gestation period normally is about 25 days but is extended to about 36 days after postpartum mating. Litter size in captivity was 2-5 young, weaning occurred at around 3 weeks, and females first conceived at 3.0-3.5 months.
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