Passive Winter and Active Spring: Variation in the Cave-Exiting Activity of Bats in the Central Himalayas of Nepal

Bats spend a significant portion of their time roosting inside caves, where they can enter daily torpor or hibernation as an energy-saving strategy. Between torpor bouts, bats may awaken and emerge to rehydrate, forage, or switch roosts. Such activities are closely linked to species-specific responses that are triggered by changes in surface-level temperatures. Climate warming can, thus, alter bat emergence behaviors, with potentially more pronounced effects in regions like the central Himalayas, where climate warming exceeds the global average. However, emergence patterns from cave systems in this region are understudied, with limited information available to monitor future changes in such behaviors. To address this gap, we examined an elevational gradient across three different seasonal phases to quantify variations in cave emergence activity in the central Himalayas. A total of 23 caves were surveyed using acoustic monitors along an elevational gradient (400–2700 m) during mid-winter, late winter, and early spring. Overall, bat emergence activity was significantly greater in late winter and early spring compared to mid-winter. During mid-winter, activity was only observed in caves in the lower elevation. In late winter and early spring, emergence activity increased across all elevations, although activity levels varied between species. These findings provide a baseline for long-term monitoring of bat emergence activity in the central Himalayas as winters continue to warm due to climate change.