Oregon state officials are taking innovative steps to avoid evicting colonies of Townsend’s big-eared bats that have been roosting in a pair of aging Interstate 5 bridges that have just been replaced near Eugene. As built, the new bridges just won’t accommodate the bats, the Eugene Register Guard reports, so special “bat boxes” are being added.
The bats were seen flying out from beneath the older bridges when they came out to hunt insects on summer nights, and officials confirmed that the bats were using the bridges for summer roosting, the newspaper said. Townsend’s big-eared bats occur over most of the American West, but they are susceptible to human disturbance and their numbers are reported to be declining in Oregon and elsewhere.
Register Guard reporter Laura Ruggeri wrote that “the bottoms of older bridges are generally rough in texture, giving bats something to grip onto and an inviting place to hang. The older bridges … also had hollow beams where bats liked to roost, said Jyll Smith,” a bridge specialist with the state Department of Transportation.”
The newer bridges don’t have the same features, so the bat boxes, designed by a team of transportation and wildlife officials, may be the best chance for luring the bats back in the spring, Ruggeri wrote.
In order to create cavern-like spaces for the bats, concrete panels were laid into the steel I-beams at the bottom of the bridges, Art Martin of the Fish and Wildlife Department told the newspaper. Then plywood or concrete baffles with gaps large enough for the bats were added. At least four of the box-like structures were added to each bridge. Hamilton Construction of Springfield, lead contractor for the bridge project, voluntarily covered the cost of the bat boxes, Smith said.
Smith told the Register Guard that the Transportation Department will monitor the boxes to determine whether the bats will use them and, if so, similar structures could be placed beneath other Oregon bridges.
But they won’t know the answers before spring. Martin notes that Townsend’s big-eared bats hibernate in winter and the bridges were never suitable for hibernation because of unstable temperatures. The bats must have found other accommodations for the winter, but they are likely to return in spring. That’s when officials will learn whether the bats will accept their new homes.