The effect of ambient temperature on the arousal frequency of the hibernating Greater horseshoe bat, Rhinolophus fermmequinum, in relation to site selection and the hibernation state



Undisturbed hibernating Greater horseshoe bats were studied over three winters to find the effect of temperature on arousal frequency, timing of arousals and the selection of a hibernation site. The study showed that temperature is important in all three aspects and the ability to select a temperature zone accurately is an important factor in the survival of hibernation by a bat.

The arousal frequency falls with falling ambient temperature then seems to rise again below 6°C. There is a clear seasonal effect, bats waking up on average once a day at 10.5°C in winter compared with 8.5°C in spring. An arousal frequency of once in six days occurs at 8°C in winter compared with 6°C in spring. This shift of 2°C is compensated for by a shift of 2°C in temperature selection by the bats in relation to the same external climatic temperatures on the day of arousal. It appears that bats may select the temperature zone which, if prolonged, will result in the most advantageous arousal frequency in relation to feeding experiences.

The seasonal effect discovered indicates that inhibition of the arousal process is important in hibernation and a hormone is postulated.