May 2005, Volume 3, Issue 5

Sand Gives Bat Houses a New Twist

By Mark & Selena Kiser

One drawback to conventional bat houses is that temperatures inside the roost chambers can sometimes fluctuate dramatically, forcing bats to expend considerable energy in order to maintain their body temperature. In an effort to create a more thermally-stable bat house, Bat Conservation International helped Marvin Maberry of Maberry Centre Bat Homes design and test a new type of bat house. Maberry, an innovative bat house manufacturer and long-time volunteer with BCI’s Bat House Project, developed a prototype in fall 2002 called the Belfry Tower II “Sand Box.” This was a plastic-stucco rocket-style house with a unique feature--an outer reservoir at the top (surrounding the upper roosting area) that could be filled with 12 pounds of dry sand. The first Sand Box was occupied by two big brown bats (Eptesicus fuscus) the first night after installation in Cason, Texas and the colony grew to 30 bats within six months.

Several more of these prototype houses were shipped to other test sites for comparison with similar plastic-stucco rocket boxes (without sand) built by Maberry. Kent Borcherding, a veteran bat house volunteer in Wisconsin, observed up to 30 little brown myotis (Myotis lucifugus) in a Sand Box in summer 2003, and by summer 2004, there were more than 100, compared with 20 to 80 bats each in the adjacent, unmodified rocket boxes.

In 2003, volunteer Patricia Otto in northwestern Washington observed that her Sand Box received greater use by a colony of long-eared myotis (Myotis evotis) than three other plastic-stucco rocket boxes and four of her six wooden rocket boxes. Nearly two-thirds of her bat colony used the Sand Box in July, and bats used this house continuously from the end of May through August. The other nine boxes were only used a few days or weeks at a time.

The only downside to Maberry’s prototype was that it was more fragile than his other Belfry Tower models and often damaged in shipment. He went back to the drawing board and designed two additional houses, one that holds six pounds of sand in tubes on the inside (“4-tube Sand House,” see below), and another (“Sand Box II”) that holds 11 1/2 pounds of sand in an internal cavity surrounding the upper roosting area. In November 2004 at Marvin’s home, he observed more bats in his “4-tube Sand Houses” than his standard Belfry Tower houses, presumably due to the added temperature stability. If you are interested in receiving more information about these models, please contact Marvin Maberry at

Sand-filled rocket boxes (“4-tube Sand Houses”) undergoing temperature experiments at Maberry Centre Bat Homes facility, Daingerfield, Texas. Photo courtesy of Marvin Maberry

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