Effects of Disturbance on the Energy Expenditure of Hibernating Bats

Abstract

(1) We investigated the effects of a range of stimuli, associated with disturbance by visitors to caves, on the energy expenditure of hibernating bats. (2) Twenty-five individual bats of six species were exposed to 206 separate applications of non-tactile stimuli (head torch, photographic flash, sound, speech, temperature increase). This resulted in only nine significant increases in energy expenditure (4.4%). In contrast, nineteen out of nineteen tactile stimuli, applied to ten individuals of four species, resulted in significant increases in energy expenditure. The difference in frequency of response to the two types of stimulation was highly significant. (3) The extra energy expended by bats in a response following a non-tactile stimulation was low (mean=49 J). Tactile stimulation resulted in much greater energy expenditure (mean= 2038 J). (4) Neither the degree nor the frequency of response to non-tactile stimulation was affected by species, body mass, ambient temperature, season, or metabolic rate during torpor. Degree of response to tactile stimulation increased significantly with increasing body mass. (5) Energy expenditure during torpor (pre-stimulation) was significantly affected by temperature in Natterer's bat (Myotis nattereri Kuhl), Daubenton's bat (Myotis daubentoni Kuhl), brown long-eared bats (Plecotus auritus L.), and by body mass in these species and pipistrelles (Pipistrellus pipistrellus Schreber). The mean energy expenditure across all species was 6-17mW. (6) By combining the measured energy expenditure in torpor before stimulation with the increase in energy requirements which accompanied non-tactile and tactile disturbance, the mean maximum reduction in potential duration of hibernation resulting from a non-tactile disturbance which elicited a significant response was 4-5h, and was 104h for each tactile disturbance. (7) Each non-tactile disturbance was predicted to decrease fat stores by 0001 g. Each tactile disturbance was predicted to decrease fat stores by 005 g.