Building a better bat box: Temperature variation in rocket box designs

 

https://www.eurekalert.org/news-releases/938281

 

  News Release 16-Dec-2021
Peer-Reviewed Publication
University of Illinois College of Agricultural, Consumer and Environmental Sciences

Bat box designs vary widely, but many commercial varieties remain untested and risk cooking the animals they’re designed to shelter. Often small and painted dark colors, these boxes may rise to dangerous temperatures on sunny days in summer, putting mom and pup in harm’s way.

New research from the University of Illinois shows a four-sided “rocket box” style, especially with modifications to length and insulation, provides more thermally appropriate roosting spaces for bats. Diverging from earlier bat box research, the study meticulously maps hot spots inside more than a dozen rocket box designs.

“Previous work made broad temperature comparisons among a hodgepodge of bat box designs, usually at only one spot inside the box. In those kinds of studies, it’s hard to know the full temperature gradient bats experience or which design elements are most important for maintaining optimal temperatures,” says Joy O’Keefe, an assistant professor and wildlife extension specialist in the Department of Natural Resources and Environmental Sciences at Illinois.

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“A rocket box can hold more than 200 Indiana bats; such a mass of warm bodies could increase roost temperatures from stressful to lethal on hot days,” says study author Frank Tillman, former graduate researcher working with O’Keefe.

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“When a bat chooses a box near sunrise, they all pretty much look the same. They're all cold. So the bats can't really know what they're getting into. Then, by the middle of the day, temperatures are starting to get comfortable. Everybody's hunky dory. It’s the end of the day where you can get these deadly temperatures. We've seen temperatures in the bat boxes being 68 degrees Fahrenheit higher than the outside air temperature,” O’Keefe says.

Generally, the tops of the boxes were heating up more and faster than the middle and bottom portions. But because rocket boxes are long and four-sided, bats could theoretically move vertically or away from sun-blasted sides of the box. A longer box, like the 1.5-meter-long design tested in the experiment, would offer a greater range of temperatures.

Another winning design was a water jacket design dreamed up by co-author George Bakken, an emeritus professor at Indiana State University. This design had a layer of vacuum-sealed water bags inserted in a sleeve around the standard rocket box. The water acts as a buffer, effectively moderating daily temperature fluctuations and making it less likely for the box to reach extremely hot or cold temperatures.

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