Energy and Water Metabolism of Free‐Ranging Pocket Gophers, Thomomys Bottae

Seasonal influences on the patterns of energy and H 2 O metabolism by free—ranging pocket gophers, Thomomys bottae, were investigated using 3 HH 1 8 O procedures. Metabolic rates of adult, nonreproductive gophers did not differ significantly in summer, winter, or spring (CO 2 , 2.34 mL°g — 1 °h — 1 ; 1416kJ°kg — 1 °d — 1 ). Efficiency of energy assimilation (54%) by gophers consuming natural diets in the laboratory did not differ between summer and winter, even though composition of the diet changed seasonally. Calculated feeding rates (dry food, 119g°kg — 1 °d — 1 ), also did not differ with season. Harvesting rates were more than two times feeding rates. Construction of energy budgets revealed that if annual vegetation is abundant, precluding the necessity for gophers to burrow extensively for food, energy is not limiting in any season. Gophers remained in H 2 O balance (influx ° efflux) in all seasons. However, influx was significantly greater during spring (518 mL°kg — 1 °d — 1 ) than during summer or winter (256 mL°kg — 1 °d — 1 ). In freeranging gophers, H 2 O influx was three to six times the minimum H 2 O flux of gophers that were maintained on H 2 O—restricted diets in the laboratory. In spite of their existence in arid macroenvironments, gophers appear to be "H 2 O—dependent." Diet selection and occupation of humid burrow systems appear to be prerequisites for existence in such habitats.