Overview: Bat boxes as a conservation tool—and a potential risk
Artificial roosts for bats, commonly known as bat boxes, are widely used to conserve native species where natural hollows are scarce. In urban areas, they offer shelter after large trees with hollows have been removed. However, researchers warn that poorly designed and deployed boxes can become death traps during hot weather, particularly in heatwaves. A study published in the Journal of Experimental Biology highlights temperatures inside bat boxes that can reach deadly levels, underscoring the need for thoughtful construction and placement.
The Canadian study: what was found
The research focused on big brown bats (Eptesicus fuscus) in Lillooet, western Canada. Lead author Ruvinda de Mel, a PhD candidate at the University of Newcastle, emphasized the community’s commitment to bat conservation while acknowledging the risks. The team captured 22 bats (11 female, 11 male) and observed them under varying temperatures in a field laboratory, tracking breath, carbon dioxide exhalation, and water loss to estimate how long a bat could endure higher heat.
Simultaneously, researchers monitored existing bat boxes during a summer month. While that month’s temperatures inside boxes were initially safe, the data allowed predictions for past heatwaves. The shocking result: boxes could exceed 50°C during heatwaves, a level potentially lethal for bats. Even temperatures around 40°C, persisting for hours, pose serious threats. These findings suggest that putative refuges can transform into ecological traps when ambient conditions are extreme.
How this fits into a broader climate context
Ecologists argue that the study’s approach—linking physiological data with environmental conditions—offers a powerful framework for understanding how bats will cope with a rapidly changing climate. Dr. Christopher Turbill of the University of Western Sydney praised the work for its integration of physiology and environment, noting it enables firm predictions about bat responses to warming conditions.
Implications for Australian bats
While the study was conducted in Canada, its implications resonate in Australia. Ruvinda de Mel notes that different bat species have distinct physiological limits. Australia has recorded bat deaths linked to heat in bat boxes and several mass die-offs during heatwaves. Ecologist Shannon Currie of the University of Melbourne explains that Australian bats often rely on very old trees for roosts, as hollows form with age in eucalypts. This makes roost selection highly sensitive to temperature and sunlight exposure, highlighting a risk that climate change could render natural roosts similarly dangerous.
Practical steps to safer bat boxes
Despite the findings, bat boxes remain a valuable conservation tool when designed and placed with care. Practical recommendations include:
- Paint boxes white or light colors to reflect sunlight and reduce heat absorption.
- Place boxes in shaded or partially shaded locations to avoid extreme heat buildup.
- Shift from traditional bat boxes to “bat condos” with multiple internal temperature zones, chimneys, or staggered insulation to offer different thermal options.
- Provide varied materials and orientations on trees or structures to grant roosting choices and reduce overheating risk.
- Preserve old trees when possible, as their hollows support a wide range of wildlife, including bats.
- Maintain insect-friendly gardens to ensure a robust food supply for bats, supporting overall ecosystem health.
“It’s a case of providing the bat choice within that artificial structure,” de Mel said. Dr. Currie concurs that diversity in roost materials and placements is key to safer, more effective urban bat conservation.
Conclusion: a cautiously optimistic path forward
Bat boxes remain a critical conservation tool when best practices are followed. By acknowledging the heat risk and implementing thoughtful design and placement, communities can support bat populations while mitigating the danger of ecological traps in a warming world.
