Habitat quality, torpor expression and pathogen transmission in little brown bats (Myotis lucifugus)

Abstract

Protection of habitat can improve survival and reproductive fitness of threatened and endangered wildlife, particularly if that habitat helps individuals maintain energy balance. Temperate bats are heterothermic and rely on torpor to save energy during winter hibernation and, to a lesser extent, during summer. However, torpor delays parturition and slows lactation for females, and inhibits sperm production for males, so reproductive bats should select warm roosts to help them avoid torpor. Torpor may also slow healing rates, which could have implications for bats that survive the winter with white-nose syndrome (WNS), a devastating fungal skin disease impacting hibernating North American bats. WNS survivors must emerge from hibernation and initiate reproduction while also healing from extensive wing damage caused by the disease. Warm roosting habitat could help WNS survivors avoid torpor to heal and reproduce more quickly, enhancing population recoveries. However, reduced torpor expression and increased activity and exploration could increase the chance of bats acquiring pathogens and parasites from substrates in their environment. I tested the hypotheses that warm roosting habitat: 1) reduces use of torpor by endangered little brown bats (Myotis lucifugus); but 2) increases the risk of pathogen acquisition from substrates in the environment. I captured bats from a fall swarm and housed individuals in outdoor flight enclosures equipped with either four heated or four unheated roost boxes. I quantified torpor expression using skin temperature dataloggers and used ultraviolet (UV) fluorescent powder as a proxy pathogen which I applied to one of the four roost boxes in each tent. Bats provided with warm roosts used less torpor (p<0.0001), but the amount of time a bat spent in torpor (p=0.26), had no effect on intensity of infection with the proxy pathogen. My data highlight roost temperature as a driver of torpor expression in little brown bats but suggest that heated roosts will not speed rates of pathogen or parasite acquisition from the environment. This result supports the potential of enhancement of summer roosting habitat as a management strategy for WNS.