Evaluation of the accuracy of body temperature measurement using external radio transmitters

The facultative depression of body temperature represents an important energy strategy for small homeotherms. However, measuring body temperature under field conditions by means other than externally attached temperature-sensitive radio transmitters is problematical. We show that skin temperatures measured by external radio transmitters can accurately reflect core temperature for the bat Carollia perspicillata. We compared body and skin temperatures at three ambient temperatures (T-a; 21, 26, and 31 degrees C). The difference between skin and body temperature (Delta T) was linearly correlated with T-a and can be predicted by Delta T = 4.395 - 0.118T(a). We argue that external temperature-sensitive radio transmitters can provide a reliable index of core temperature and so permit the study of torpor or facultative hypothermia under field conditions.