Temperature variation in rocket box designs

Bat box designs vary widely, but many commercial varieties remain untested and risk cooking the animals they are designed to house. Often small in size and painted in dark colors, these boxes can rise to dangerous temperatures on sunny days in summer, putting the mother and puppies at risk.

New research from the University of Illinois shows that the four-sided “rocket box” pattern, especially with modifications to length and insulation, provides thermally suitable perching spaces for bats. The study differs from previous bat box research, in that the study precisely identifies hot spots within more than a dozen missile box designs.

“Previous work has performed extensive temperature comparisons between a range of bat box designs, usually in just one location within the box. In these types of studies, it is difficult to know what full temperature graded bat experience or design elements are most important to maintaining optimal level,” says Joy O’Keeffe. , assistant professor and specialist in wildlife guidance in the Illinois Department of Natural Resources and Environmental Sciences, “Temperatures.”

The O’Keefe team built 19 custom rocket boxes, including a standard design: a one-meter-long, four-sided box with two vertical chambers on each side. In each of the 18 variations, they added or removed air vents; change of building materials, roof design and overall length; Added different buffer jackets. They also built a standard three-chamber flat facade design such as 20^y point of comparison.

In each box, the researchers placed 12 temperature sensors at the top, middle, and bottom of the outer chamber on each side of the box.

“There are some studies that put a sensor in each room in a three-chamber box, or put sensors at the top and bottom of one design. But we have top to bottom in all four cardinal directions, so it’s really unique,” ​​says O’Keefe.

The researchers placed the boxes atop 16-foot poles along a gravel road in a wooded and agricultural area in Indiana. The new apartment complex in the neighborhood may have been the talk of the resident bat colony, but unfortunately, bats were excluded from the boxes for the duration of the experiment, allowing the researchers to understand temperature gradients without the complexity of body heat.

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

The team recorded temperatures 24 hours a day, counting the times when temperatures were cool, permissive (comfortable), and exhausting. They also measured external conditions, such as solar radiation and wind speed.

Over the course of the day, conditions inside the chests changed dramatically.

“When a bat picks out a box near sunrise, they all look pretty much the same. They’re all cold. So the bats can’t really tell what they’re getting into. Then, by midday, the temperatures are starting to feel good. Everyone is great. It’s The end of the day where you can get these killer temperatures. We’ve seen temperatures in bat boxes 68 degrees Fahrenheit higher than the temperature outside,” says O’Keefe.

In general, the tops of the boxes were heated faster than the middle and lower ones. But because rocket boxes are tall and four-sided, bats can theoretically move vertically or away from the sides of the box that have been exposed to sunlight. A taller box, such as the 1.5-meter design tested in the experiment, will provide a greater range of temperatures.

Another winning design was a water jacket design dreamed up by co-author George Bakken, professor emeritus at Indiana State University. This design had a layer of water-tight bags that were inserted into a casing around the standard missile box. The water acts as a buffer, effectively mitigating daily temperature fluctuations and reducing the possibility of the box reaching temperatures that are either too cold or too hot.

“When the outside temperature drops below freezing, the inside of the box should remain above freezing, protecting the bats, until the water in the casing freezes,” Bakken says. “We calculated that it would take two days for the jacket to freeze after the outside air temperature had dropped to freezing.”

This is especially important for young puppies and nursing females who need to spend less energy warming themselves. It’s also important in the spring, when bats come out of hibernation. Oftentimes, they develop the devastating fungal disease White Nose Syndrome during their winter sleep and are in a rough state when they emerge for the season.

“If they can come out of hibernation and go to hot roosts, they will be better able to recover and not have to expend as much energy trying to stay warm. But you can’t really turn off electricity in the landscape to save hot roosts for bats,” says O’Keefe. That’s why we envisioned the water jacket design.”

Ultimately, many of the boxes reduced the risk of overheating or provided space for bats to move around and avoid extreme temperatures. O’Keefe says there is still a lot of experimentation to be done, especially with so-called thermal lag designs like the water jacket. But in the meantime, she has a website that offers tips for making bat boxes safer for bats.

The search was published in Environmental Evidence and Solutions.