Winter torpor patterns of tricolored bats (<i>Perimyotis subflavus</i>) in the southeastern United States

Abstract The Tricolored Bat (Perimyotis subflavus) has suffered significant population declines in much of its geographic range due to white-nose syndrome (WNS). Our aim was to describe the torpor patterns of tricolored bats within the southeastern United States to further our understanding of their winter ecology and potential susceptibility to WNS in currently unimpacted areas based on data from bats in both a WNS-affected hibernaculum and an unaffected hibernaculum. We placed temperature-sensitive radio transmitters on tricolored bats in a site in northwestern South Carolina that was WNS-positive and another site in northwestern Florida that was WNS-negative, and determined torpid and arousal skin temperatures (TSK), torpor bout duration (TBD), and arousal duration (AD) during 3 winters. Mean hibernacula temperature (TH) and vapor pressure deficit (VPDH) in both hibernacula were within the range of optimal Pseudogymnoascus destructans (Pd) growth (TH = 12.7 to 13.6 °C, VPDH = 0.028 to 0.059 kPA). Mean torpid TSK was 15.7 ± 0.1 °C and mean TBD was 4.1 ± 0.2 days across sites. Sex was the best predictor of TBD with males having significantly longer TBD than females. Torpid TSK was positively related to TH and negatively related to VPDH. Because the TSK of a bat was similar to the optimal growth temperatures of Pd, our findings suggest that even though winters in the southeastern United States are more benign than in other parts of the Tricolored Bat range, the warmer temperatures in southern hibernacula may provide optimal conditions for the growth of Pd. Greater understanding of the physiological responses of tricolored bats in hibernacula across their range will provide important data on the potential for WNS morbidity and mortality in unaffected areas and allow for a better distribution of resources for prevention and treatment of WNS.