Temporal Changes in Body Mass and Body Condition of Cave-Hibernating Bats During Staging and Swarming

Abstract

Abstract The rapid colonization of the Pseudogymnoascus destructans fungus across cave systems in eastern North America and the associated bat mortalities (white-nose syndrome; WNS), necessitates studies of cave-hibernating bats that remain unaffected by, or in close proximity to, the leading edge of the fungal distribution to provide baseline predisturbance data from which to assess changes due to fungal effects. Studies of the physiological ecology of cave-hibernating bats during the spring staging and autumn swarming seasons are few, and an understanding of patterns in body condition of bats associated with entry into and emergence from hibernation is incomplete. We sampled bats at the entrance to a cave in Mammoth Cave National Park, Kentucky, during swarming and staging, prior to (2011 and 2012), concurrent with (2013), and following (2014) the arrival of the WNS fungus. We evaluated seasonal and annual changes in body mass and body condition of bats entering and leaving the cave. We captured 1,232 bats of eight species. Sex ratios of all species were male-biased. Capture success was substantially reduced in 2014, following the second winter after arrival of the WNS fungus. Significant temporal variation in body mass and body mass index was observed for little brown bats Myotis lucifugus, northern long-eared bats M. septentrionalis, and tri-colored bats Perimyotis subflavus, but not Indiana bats M. sodalis. Little brown bats and northern long-eared bats demonstrated significant increases in mean body mass index in 2014; this pattern likely reflected a relatively better body condition in bats that survived exposure to the WNS fungus. Most species demonstrated highest body mass and body mass index values in late swarming compared with other sampling periods, with tri-colored bats showing the greatest percent increase in body mass (42.5%) and body mass index (42.9%) prior to entering hibernation. These data indicate significant intraspecific variation in body condition of cave-hibernating bat species, both among years and between the seasons of autumn swarming and spring staging. We suggest this variation is likely to have implications for the relative vulnerability of species to WNS infection across the distribution of the Pseudogymnoascus fungus.