The ecology of eastern small-footed bats at Shenandoah National Park

Abstract

Several aspects of rock-dwelling eastern small-footed bat (Myotis leibii) ecology remain poorly resolved including the species' local distributions and abundance within their range, maternity habits, and thermoregulatory strategies. Broadly rare, eastern small-footed bats appear to be largely localized to mountainous habitats that feature their preferred roosting habitat, emergent rock features and talus slopes. Following initial reports of mortality from the bat epidemic white-nose syndrome, eastern small-footed bats were reviewed for protection under the endangered species act but were rejected due to lack of significant evidence of declines and overall understanding of their broadscale abundance. In response, a novel method of conducting visual searches of rock outcrops and talus slopes was developed to detect the presence of summer day-roosting eastern small-footed bats. I explored a novel methodology expanding on this technique, whereby I conducted visual searches of talus slopes at Shenandoah National Park, Virginia, modeled bat abundance by topographic variables, and predicted bat abundance to talus slopes throughout the park to talus slopes classified with algorithms utilizing high-definition imagery and a topographic index measuring terrain ruggedness. Eastern small-footed bats were widespread and relatively abundant at Shenandoah National Park, occurring in the majority of sampled talus slopes and topographic conditions. The top abundance model included covariates aspect, elevation, topographic exposure index (TEI), vector ruggedness measure (VRM), and talus area and had a pseudo R-squared of 0.58. Aspect, elevation, VRM, and area positively influenced bat abundance, whereas TEI negatively influenced abundance. Eastern small-footed bats were most abundant in positions with increased solar exposure, which drove model performance. The abundance model estimated 1,330 eastern small -footed bats roosting in talus slopes throughout Shenandoah National Park. I also documented the phenology, roost use, thermoregulatory patterns, and roost and social network dynamics and of a maternity colony of eastern small-footed bats. Eastern small-footed bat females formed a cohesive social network that used rock crevice roosts in a fission-fusion dynamic similar to tree-roosting bat species, exhibiting similar network dynamics centralized to a primary, central node roost. Natality was high and all females were either pregnant or lactating. Parturition occurred synchronously in mid-June. The maternity colony was philopatric to a large talus slope receiving high solar exposure and featuring large boulders and a dense concentration of large crevices. To evaluate thermoregulatory ecology and foraging activity periods, I used temperature-sensing radio transmitters to record bat skin temperatures pregnant and lactating eastern small-footed bats. All bats engaged in torpor every day but pregnant and lactating eastern small-footed bats engaged in distinctly different thermoregulatory patterns, in which pregnant bats generally used shallower torpor and shorter torpor periods compared to lactating bats that more frequently engaged in deep torpor. These regulating and conforming thermoregulatory strategies were similar to observations of little brown bats (M. lucifugus) and suggest respective strategies offer energetic trade-offs supportive of each reproductive phase. Pregnant and lactating eastern small-footed bats also exhibited significantly differing foraging periods, in which pregnant bats left day roosts for longer continuous periods, whereas lactating bats left for short, sometimes multiple forage bouts returning to day roosts in between. Differences in foraging periods may reflect the foraging efficiency, maternal responsibilities, and energetic requirements associated with thermoregulatory strategies of each reproductive phase. Both pregnant and lactating eastern small-footed bats passively rewarmed in day roosts, supporting the importance of solar exposure to abundance model. Energetic savings from daily torpor and that likely contributes to their maternity habits, day roost selection, and spatial abundance.