Introduction: Bat boxes as a conservation tool—and a potential hazard
Artificial roosts for bats, commonly known as bat boxes, are widely used to support native bat populations where natural habitats have been degraded or removed. In urban areas, these boxes offer shelter when hollow trees are scarce. A new study in the Journal of Experimental Biology raises a warning: if bat boxes are not carefully designed and placed, they can become deadly roosts during heatwaves.
What the study found
Researchers in Canada tested big brown bats (Eptesicus fuscus) in Lillooet, western Canada. They measured how bats breathed, exhaled carbon dioxide, and lost water at different temperatures to determine how long a bat could endure extreme heat. Simultaneously, they recorded temperatures inside existing bat boxes during the same season. The results were alarming: bat boxes could exceed 50b0C during heatwaves, a lethal level for bats. Even temperatures around 40b0C—sustained for hours—pose serious risks.
Why this matters beyond Canada
Although the fieldwork was conducted in Canada, the authors note that heat-related bat deaths have also occurred in Australia. The finding that roosts can act as ecological traps under rising temperatures is a global concern, especially as climate change intensifies heatwaves in many regions.
Implications for bat species in different regions
Experts emphasize that physiological limits vary across bat species. In Australia, for example, many bats depend on old trees that develop hollows as they age, and salients such as sun exposure influence roost choice. Ecologists warn that as climate change accelerates, traditional roost sites could become dangerously hot, forcing bats to seek alternative microclimates that may not exist in urbanized landscapes.
Designing safer bat roosts: practical recommendations
Despite the risks uncovered by the study, bat boxes remain a valuable conservation tool if designed with safety in mind. The researchers offer several practical strategies to reduce heat stress:
- Paint bat boxes white or light-colored to reflect sunlight and lower internal temperatures.
- Position roosts in shaded or partially shaded locations to avoid peak heat.
- Adopt a “bat condo” approach—structures with multiple internal temperatures and zones, achieved by varied insulation, chimneys, or strategic exposure to sunlight.
- Provide a diversity of roosting options and orientations on trees or near homes to give bats varied thermal microclimates.
- Preserve old trees where possible, as they remain valuable for many species beyond bats.
Dr. Shannon Currie, an ecologist in Australia not involved in the study, supports the idea of varied materials and orientations to create flexible roosts. She notes that maintaining old trees and planting insect-friendly gardens can bolster food resources, helping bats survive extreme conditions.
Looking ahead: research and adaptation
The lead researcher, PhD candidate Ruvinda de Mel, is expanding his work to model how different bat species tolerate various roosting conditions. Ecologists like Christopher Turbill commend the study for integrating physiological data with environmental measures, a combination that strengthens climate-adaptation predictions for bats. The overarching message is clear: as temperatures rise, thoughtful roost design and habitat diversity are essential to prevent roosts from becoming ecological traps.
Conclusion: safeguards that enable coexistence
Bat boxes can continue to support bat populations, provided they are designed, placed, and maintained with temperature dynamics in mind. By combining white sun-reflective surfaces, shaded placements, multi-temperature roosts, and a landscape that includes old trees and insect-rich gardens, communities can offer safe refuges for bats while promoting broader biodiversity.
