Conspecific disturbance contributes to altered hibernation patterns in bats with white-nose syndrome

The emerging wildlife disease white-nose syndrome (WNS) affects both physiology and behaviour of hibernatingbats. Infection with the fungal pathogen Pseudogymnoascus destructans (Pd), the first pathogen known to targettorpid animals, causes an increase in arousal frequency during hibernation, and therefore premature depletion ofenergy stores. Infected bats also show a dramatic decrease in clustering behaviour over the winter. To investigatethe interaction between disease progression and torpor expression we quantified physiological (i.e., timing ofarousal, rewarming rate) and behavioural (i.e., arousal synchronisation, clustering) aspects of rewarming eventsover four months in little brown bats (Myotis lucifugus) experimentally inoculated with Pd. We tested two competing hypotheses: 1) Bats adjust arousal physiology adaptively to help compensate for an increase in energetically expensive arousals. This hypothesis predicts that infected bats should increase synchronisation of arousalswith colony mates to benefit from social thermoregulation and/or that solitary bats will exhibit faster rewarmingrates than clustered individuals because rewarming costs fall as rewarming rate increases. 2) As for the increasein arousal frequency, changes in arousal physiology and clustering behaviour are maladaptive consequences ofinfection. This hypothesis predicts no effect of infection or clustering behaviour on rewarming rate and that disturbance by normothermic bats contributes to the overall increase in arousal frequency. We found that arousalsof infected bats became more synchronised than those of controls as hibernation progressed but the pattern wasnot consistent with social thermoregulation. When a bat rewarmed from torpor, it was often followed in sequence by up to seven other bats in an arousal “cascade”. Moreover, rewarming rate did not differ between infected and uninfected bats, was not affected by clustering and did not change over time. Our results supportour second hypothesis and suggest that disturbance, not social thermoregulation, explains the increased synchronisation of arousals. Negative pathophysiological effects of WNS on energy conservation may therefore becompounded by maladaptive changes in behaviour of the bats, accelerating fat depletion and starvation.