Winter torpor and body mass patterns of a cave-roosting bat in cool and warm climates

Torpor is an important energy-saving strategy for small insectivorous bats during winter. White-nose syndrome (WNS), a fungal disease affecting hibernating bats, disrupts torpor-arousal patterns and increases energy use, leading to higher winter mortality. In North America, WNS has also infected bats in milder southern climates, supporting concerns about potential impacts if introduced to the Southern Hemisphere. To understand the winter hibernation ecology and sensitivity to WNS of cave-roosting bats, we used temperature telemetry to study torpor patterns and body mass change of the eastern bent-winged bat (Miniopterus orianae oceanensis) at a cold and warm site (mean annual surface temperature 11.7 and 17.8 °C, respectively) in southeastern Australia during winter. Torpor bouts were 4.6 times longer at the cold site (30.8 ± 21.4 h, max = 304.8 h) than at the warm site (6.7 ± 3.8 h, max = 46.5 h), and normothermia duration was longer at the warm site (7.8 ± 3.6 h) than at the cold site (6.6 ± 2.9 h). Torpor bout duration, probability of arousal, and normothermia duration were influenced by nightly weather and season. Mean overwinter body mass loss was twice as high at the cold site (3.1 g) than at the warm site (1.2 g), likely reflecting overwinter food availability. This study provides insights into bat hibernation in mild climates where WNS poses a threat, suggesting that similarities in overwinter torpor and body mass loss to North American species in similar climates may indicate a risk of reduced winter survival for some Australian cave-roosting bat species.