SUMMARY Many species hibernate to conserve energy during periods of low food and water availability. It has long been assumed that the optimal hibernation strategy involves long, deep bouts of torpor that minimize energy expenditure. However, hibernation has ecological (e.g. decreased predator avoidance) and physiological (e.g. sleep deprivation) costs that must be balanced with energy savings; therefore, individuals possessing sufficient energy reserves may reduce their use of deep torpor. We tested the hypothesis that energy (fat)availability influences temperature selection of two fat-storing bat species during hibernation. We predicted that individuals with small energy reserves would select colder temperatures for hibernation in order to minimize energy expenditure, while individuals with larger energy reserves would choose warmer temperatures to minimize the costs of hibernation. Results from our field experiment indicate that little brown myotis (Myotis lucifugus)hibernating in warm microclimates were significantly heavier than individuals hibernating in cooler microclimates. To determine if energy availability was mediating this relationship, we limited fatty acid availability with mercaptoacetate (MA) and quantified its effect on torpid metabolic rate(TMR) and thermal preference of big brown bats (Eptesicus fuscus). Administration of MA caused a 43% drop in TMR at 10°C and caused bats to choose significantly colder temperatures for hibernation. Our results suggest that fat-storing bats minimize torpor expression using both physiological and behavioral mechanisms.

Although it has been widely documented that populations of cave-roosting bats rapidly decline following the arrival of white-nose syndrome (WNS), longer term reproductive effects are less well-known and essentially unexplored at the community scale. In West Virginia, WNS was first detected in the eastern portion of the state in 2009 and winter mortality was documented in 2009 and 2010. However, quantitative impacts on summer bat communities remained unknown. We compared “historical” (pre-WNS) capture records and reproductive rates from 11,734 bats captured during summer (15 May to 15 August) of 1997–2008 and 1,304 captures during 2010. We predicted that capture rates (number of individuals captured/net-night) would decrease in 2010. We also expected the energetic strain of WNS would cause delayed or reduced reproduction, as denoted by a greater proportion of pregnant or lactating females later in the summer and a lower relative proportion of juvenile captures in the mid–late summer. We found a dramatic decline in capture rates of little brown Myotis lucifugus, northern long-eared M. septentrionalis, small-footed M. leibii, Indiana M. sodalis, tri-colored Perimyotis subflavus, and hoary Lasiurus cinereus bats after detection of WNS in 2009. For these six species, 2010 capture rates were 10–37% of pre-WNS rates. Conversely, capture rates of big brown bats Eptesicus fuscus increased by 17% in 2010, whereas capture rates of eastern red bats Lasiurus borealis did not change. Together, big brown and eastern red bats were 58% of all 2010 captures but only 11% of pre-WNS captures. Reproductive data from 12,314 bats showed shifts in pregnancy and lactation dates, and an overall narrowing in the windows of time of each reproductive event, for northern-long-eared and little brown bats. Additionally, the proportion of juvenile captures declined in 2010 for these species. In contrast, lactation and pregnancy rates of big brown and eastern red bats, and the proportion of juveniles, were similar to historical patterns. Our results further elucidate the significance of short-term effects and provide a basis to examine long-term consequences of WNS.