SEASONAL WATER INFLUX AND ENERGY-EXPENDITURE OF FREE-LIVING FAT SAND RATS

Free-living fat sand rats (Psammomys obesus) consumed only saltbush (Atriplex halimus), did not drink water, and maintained constant body mass in summer and winter. Rates of water influx and energy expenditure of adults were greater in winter than in summer. Daily intake of dry matter by adults ranged from 9.3 (summer) to 11.0% (winter) of body mass; intake of fresh matter ranged from 24.7 (summer) to 32.0% (winter) of body mass. Water content of A. halimus consumed by adult fat sand rats was similar in the two seasons; therefore, the increase in water influx in winter was related mainly to a greater consumption of fresh matter. Mass-specific influx of water in winter was greater in juveniles than in adults, but mass-specific expenditure of energy was similar in the two cohorts. This indicated that juveniles selected leaves of A. halimus with greater water content than did adults. intakes of dry matter and fresh matter by juveniles were 11.8 and 43.4% of their body masses, respectively.