Psammomys obesus
fat sand rat

Psammomys obesus, the fat sand rat, is found in North Africa, ranging from Mauritania to Egypt and Sudan, and east across the Arabian Peninsula. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999)

Fat sand rats are terrestrial mammals that are most often found in sandy deserts, but can be found in rocky terrain, saline-marsh areas, and loess plains. They live in burrows composed of large mouthed holes which are located near and under the bushes where they forage. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

The head and body length of P. obesus is 130 to 185mm, while the tail length is 110 to 150mm. Males weigh between 125 and 208g and females weigh between 146 and 207g. Psammomys obesus are heavily built, rat-like gerbils with fully haired and tufted tails. The tuft of hair on the end of the tail measures about 14mm. They have large, black eyes, robust limbs, and heavy feet with black 4 to 5mm claws. The skin is also black, most likely to protect them from the sun’s ultraviolet rays. The features used distinguish P. obesus are their nongrooved incisors and their very short, round ears.

Dorsal fur varies from light-brown to red to yellow and is speckled with black. The underbelly is a grayish/white, with the area under the chin slightly whiter than the rest of the ventral surface. The last third of the tail is black, including the tuft, while the underside is whitish.

Sexual dimorphism has not been noted in P. obesus. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

The lifespan of P. obesus in the wild is about 14 months while those in captivity can live between three and four years.

Fat sand rats are diurnal, with daytime activity depending on the temperature of their aboveground surroundings. In winter they may emerge for about five hours during the middle of the day. During the summer they are mainly active in the early morning and afternoon hours to avoid intense midday heat. In certain areas, fat sand rats will be active at night if the ambient temperature is warm enough. Throughout the winter they often bask in the sun, flattening their body and spreading their limbs out to absorb the heat.

Some behaviors of P. obesus are similar to those of American prairie dogs (Cynomys) in that they sit up on their hind legs and tail to observe danger and retreat to their burrows when alarmed.

It has been noted that fat sand rats use only one hand to hold their food, they wipe leaves before eating them, and comb their fur with their forefeet. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Home Range

The average home range is 189.6m^2 for males and 75.8m^2 for females. Female fat sand rats have small home ranges and tend to stay near the bushes they use for food, only moving when their food source is depleted. Like females, subordinate males also have small ranges, but they move more often than the females. Dominant males have wide ranges that may include the ranges of several females and subordinate males.

Fat sand rats have extensive burrows systems with 3-5 openings consisting of complicated tunnels with storage chambers, toilet chambers, and nests for sleeping. They are colonial, but each burrow system holds one adult with the exception of breeding when a pair or a family occupies one system. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Psammomys obesus communicate with each other using high-pitched squeaks and foot drumming. It is unknown what kinds of communications these are, though the sounds may be used to warn against predators. Fat sand rats probably also use olfactory cues extensively to communicate home range boundaries and reproductive state.

Fat sand rats have keen senses of smell, vision, and hearing. Touch can be an important way of sensing the environment and communicating with conspecifics. (Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Fat sand rats feed on the leaves of succulent plants, particularly salt bushes of the Chenopodiaceae family. Because these plants contain mostly water and salt, large amounts of leaves must be ingested in order to get enough nutrients. They can survive eating the salty plants without an abundance of water because they have extremely efficient kidneys that can excrete highly concentrated urine (about 18 times as concentrated as humans). Fat sand rats have also been known to eat grains such as barley. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Fat sand rats are preyed upon by many small predators, such as snakes, including those in the genus Spalerosophis, owls, other birds of prey, and jackals (Canis aureus). They escape predation through their vigilance, taking refuge in burrows, and through their cryptic coloration. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999)

Because fat sand rats live under and eat the leaves of Chenopodiaceae species, they may have an impact on the populations of these bushes. However, this has not been documented. Fat sand rats are an important prey base for small to medium-sized predators in the ecosystems in which they live.

Fat sand rats are known to be carriers of the parasitic disease Leishmaniasis. This disease can be transferred to humans from P. obesus by the sand fly Phlebotomus. (Mendelsshon and Yom-Tov, 1999)

Psammomys obesus can easily acquire non insulin dependent diabetes mellitus and the complications associated with diabetes (cataracts, pancreatic atrophy, and impaired renal function) from high caloric foods such as laboratory rodent pellets. For this reason, fat sand rats are used as a model species to study diabetic mellitus and its complications. (Mendelsshon and Yom-Tov, 1999; Murray et al., 2004)

Psammomy obesus does not appear to be a threatened or endangered species.