Energy metabolism and evaporative water loss in the California ground squirrel

Abstract

Rates of metabolism and evaporative water loss were investigated inSpermophilus beecheyi. Special attention was paid to the influence of the micro-climate of the animal's burrow on these parameters. Metabolic rate as measured by oxygen consumption is 25 per cent below that predicted from body weight. A new hypothesis is advanced to account for this commonly observed phenomenon in fossorial rodents. In summer, there is an overlap of the region of thermal neutrality and temperature in the animal's burrow but winter burrow temperatures are below thermal neutrality. Evaporative cooling accounts for approximately 20 per cent of the total heat loss in thermal neutrality and at low humidity. Minimization of this heat loss avenue by high humidities did not result in an increase of body temperature or metabolic rate, therefore the dimension of the thermal neutral zone is independent of ambient humidity. By indirect means, evaporative water loss was partitioned into 37 per cent from cutaneous sources and 63 per cent from pulmonary sources. A direct relationship was found between ambient water vapor pressure and evaporative water loss. The relationship between body and ambient temperature was investigated by telemetry. At lower temperatures, the former is maintained at constant levels, but hyperthermia develops above 30 ° C.