Interspecific variation in lower temperature thresholds of an assemblage of wintering bats

Abstract

Winter presents environmental and energetic challenges for temperate insectivorous bats as colder temperatures increase metabolic rates while simultaneously reducing resource availability. While bats in northern regions typically hibernate or migrate to circumvent these adverse conditions, there is growing evidence of winter bat activity as weather permits. Bats at lower latitudes may experience shorter, milder winters, increasing opportunities for activity. To better understand the relationship between ambient temperature and winter bat activity, we deployed acoustic detectors in central Louisiana and eastern Texas and examined data at 3 levels of biological organization: overall bat activity, species richness, and species-specific activity. Across 1,576 detector-nights, we recorded 37,435 bat passes. Bats responded positively to warmer temperatures but the temperature threshold for winter activity varied among species, ranging from 7.2 to 15.6 °C. Consequently, observed species richness increased at warmer ambient temperatures. With activity linked to environmental conditions in a species-specific manner, different subsets of the winter bat assemblage may be active from night to night. Additionally, our study adds to a rather limited body of literature of winter bat activity and provides a baseline for future studies as white-nose syndrome and climate change affect North American bat populations.