We studied the winter activity of bats at a site where long-term summer monitoring data has documented the presence of a diverse and abundant bat community. Acoustic monitoring at multiple locations over 4 winters (2010–2011 through 2013–2014) documented some level of activity in every species, but Myotis leibii (Eastern Small-footed Myotis) and Eptesicus fuscus (Big Brown Bat) were the only 2 species with consistent activity throughout the hibernation period. We modeled winter activity as a function of meteorological variables and the distance to both a presumed local hibernaculum and an important foraging site that we had previously documented at the New Boston Air Force Station. Based on our Random Forest model, ambient temperature was the strongest predictor of winter activity for both species; the highest rate of activity occurred when temperatures were above 12 °C. Although most of the activity occurred during the evening, we detected diurnal activity by both species throughout the winter. The fact that the 2 most abundant species during this winter study are also the 2 most common species captured during the summer suggest that these species are hibernating in close proximity to their summer range.