Deserts are regions where water and food are in short supply. Much has been learned about how desert mammals solve the problems of heat and lack ofwater, yet less is known about how desert mammals cope with food scarcity. This thesis teststhe hypothesis that desert mammals possess specialized mechanisms to reduce energy metabolism during food shortages. I selected an extreme-desert species, the golden spiny mouse (Acomys russatus) as an experimental animal. The study is divided into three parts. The first part compares the metabolic response ofspiny mice to food restriction with that of a non-desert relative, the laboratory white mouse (Mus musculus). I find that the desert mouse is able to maintain a stable body weight on half ofits normal food intake by reducing itsresting metabolism while the white mouse cannot Resting metabolism is "switched down" by 50% in a single day after about two weeks offood restriction. The "switch" is not caused by a fall in body temperature. The percent oftime spiny mice spend resting at thisreduced level gradually increases, resulting in a gradual decrease in daily metabolic rate. The second part asks whetherspiny mice can sustain theirreduced metabolism in the cold when food is in short supply. I find that when food is plentiful, spiny mice maintain a constant body temperature of 36°C over a wide range of ambient temperatures. They increase theirresting metabolic rate to keep warm when temperature falls below 32°C. However, when their food intake isreduced by 50%, they let body temperature fall to 31°C before increasing metabolism and theirthermal conductance decreases by 60%. The last part of the study asks whether the spiny mice can conserve energy when food is scarce by moving about cheaply. I find that the spiny mouse can travel nearly twice as far the white mouse on the same amount of energy, but the cost of moving about is not reduced further during food restriction. I conclude thatspiny mice do indeed possess specialized mechanisms for conserving energy in their desert environment