Temperature Regulation of Mexican Free-Tailed Bats in Cave Habitats

Abstract

The Mexican free-tailed bat, Tadarida brasiliensis mexicana , was noted in environments of 8° to 43°C and relative humidities of 10 to 100%. Large populations of bats usually occurred between 15° and 38°C and 65 to 95% relative humidity. Greatest populations were noted at 25° to 38°C. The temperatures of some Texas caves seem to be influenced by the heat given off by the bats as well as by the outside temperatures. Apparently migration is not directly related to cave temperature. Examination of body temperatures of roosting adult bats throughout the year in ambient temperatures of 12° to 36°C indicated that the subspecies usually regulates its body temperature at high levels in the wild and appears more temperature stable than many Microchiroptera that have been studied. Body temperatures of young bats (from birth until capable of flight) were well above environmental temperatures. Young bats had higher body temperatures as they became older and were at higher ambient temperatures. Regulation of the body temperature at high levels in low environmental temperatures seems to occur by increased heat production, although heat loss is apparently retarded by clustering behavior. Body temperature regulation at high cave temperatures appears to occur in the following ways: The body temperature of the bats remains below that of the deep cluster temperature by virtue of heat loss to the rocks and air which are at lower temperatures. Bats possibly move to cooler sites in the cave in times of heat stress and may separate from one another on the cave ceiling to increase heat loss. By flying and thus greatly increasing the surface area for heat loss the bats seem able to reduce their body temperatures.