Overview: bat boxes under heat stress
Artificial roosts for bats, commonly known as bat boxes, are a favored conservation tool in urban areas where hollow trees are scarce. They offer shelter for several species and help keep native bats connected to human-dominated landscapes. However, new research published in the Journal of Experimental Biology raises a crucial warning: bat boxes can reach temperatures that are deadly for bats during heatwaves unless they are carefully designed and deployed.
The study and its key findings
Researchers focused on big brown bats (Eptesicus fuscus) in Lillooet, western Canada. They captured 22 bats—an even split of females and males—and spent time with each in a field laboratory to monitor respiration and water loss at various temperatures. By tracking carbon dioxide exhalation and dehydration, they calculated how long a bat could withstand higher temperatures.
Concurrently, the team recorded temperatures inside existing bat boxes during the same summer. While current boxes appeared safe in average conditions, the data allowed the researchers to model outcomes during historical heatwaves. They found bat boxes could exceed 50°C in extreme heat, a level potentially fatal to the bats. Alarmingly, temperatures around 40°C persisting for hours also pose serious risks, creating a sustained heat trap even when averages seem tolerable.
The study’s author, PhD candidate Ruvinda de Mel, emphasized the need to rethink conservation tools in the face of climate change. “We wanted to see if this conservation tool that’s so ubiquitously used has any issues attached to it, and if there are, how we can mitigate them,” he said. The work echoes broader concerns about how warmed environments stress wildlife in anthropogenic settings.
Validation from the scientific community
Ecologist Christopher Turbill of the University of Western Sydney, not involved in the study, called the approach powerful for integrating physiology with environmental measurements. “We can make pretty firm predictions and understand the physiology behind those predictions,” he noted, underscoring how such data improves climate resilience planning for bats and other species.
Lead author de Mel is now expanding the work into more general models to help scientists predict how different bat species might cope with various roosting environments under warming conditions.
Australian context and species-specific risks
De Mel acknowledged that different bat species have distinct physiological limits. Australia, in particular, has recorded heat-related bat mortalities in bat boxes and experienced mass die-offs during heatwaves. Ecologist Shannon Currie from the University of Melbourne highlighted that Australian bats often rely on very old trees, where hollows form with age. In contrast to Europe and North America, natural roosts in Australia are closely tied to aging timber. She explained that roost selection frequently involves seeking sunlit or partial shade positions, allowing bats to respond to temperature cues.
Dr. Currie warned that climate change could render natural roosts dangerously hot, increasing reliance on artificial options that might turn ecological traps if not designed properly. There is a real concern that bats could become faithful to earlier roosts and repeatedly encounter extreme heat events.
Practical guidelines for safer bat roosts
Despite the findings, bat boxes remain a valuable conservation tool when designed with temperature regulation in mind. The researchers offer practical steps to reduce heat risks:
- Paint boxes white to reflect sunlight and lessen daytime heating.
- Place boxes in shaded locations to avoid extreme temperatures.
- Consider evolving from a simple bat box to a multi-chamber “bat condo” that provides varied internal temperatures and insulation levels.
- Incorporate features like chimneys or partial sunlight exposure to create internal temperature gradients.
Dr. Currie supports a diverse approach: “If you are providing artificial roosts, they should be made of varied materials and oriented differently to give multiple roosting opportunities.” She also advocates preserving old trees where possible, as they support a wider array of species beyond bats, and fostering insect-friendly gardens to boost food sources for roosting bats. The overarching message is simple: diversity in roosts, materials, and microclimates offers the best defense against ecological traps in a warming world.
Conclusion: balancing conservation with climate realities
The study highlights a nuanced truth: bat boxes can still be a net positive for bat conservation if we acknowledge and mitigate their heat-related risks. It’s about creating flexible roost options—roosts that can provide suitable shelter across a range of temperatures and seasons. As climate change accelerates, informed design and strategic placement will be key to ensuring that artificially provided roosts support bats rather than endanger them.
