In America, the Dutch like to say, “everything is bigger.” The cars are longer, skyscrapers are taller, even some of trees are enormous. That cliche, it turns out, applies as well to bat houses.
European bat houses grew out of the discovery that bats sometimes used bird boxes placed in forests, so bat houses on the continent almost never exceeded about 20 inches high by 12 inches wide –smaller than the bare minimum that Bat Conservation International recommends. These houses are simply too small for large nursery colonies, especially in urban areas.
But as more European bat workers encounter BCI’s Bat House Project, bat houses in Europe are changing. And Erik Korsten, chairman of the Bats Workgroup of North Brabant Province in the Netherlands, was among the first to put BCI’s research findings to the test in Europe.
He discovered about 100 common pipistrelles emerging from a damaged ventilation joint in the wall of a Tilburg Water Company building in the city of Tilburg. Company ecologist Jaap van Kemenade was delighted to have a colony of bats living in the building, but the crack they were using for a home was growing bigger and reconstruction would soon be required. Bad news for the bats.
Korsten immediately thought about the big nursery houses described in BCI’s Bat House Builder’s Handbook and figured one of them might meet the needs of the building’s pipistrelle bats. So he and some colleagues built a most unusual bat house by European standards: It is 5 feet, 11 inches wide and 3 feet, 3 inches high and featured a total of four chambers, each about three-quarters of an inch deep. The house was mounted in March 2004 to the building’s wall about three feet from the crevice roost in the wall.
Only two pipistrelles used the new bat house that first summer; the rest stuck with the old roost. But in July 2005, we counted 84 pipistrelles emerging from the bat house, with many of them returning within an hour or so, possibly to feed their youngsters.
Reconstruction work on the walls began a few days later, and by this past summer, the value of the big house was clear. We counted as many as 235 bats emerging from it, and saw many pipistrelle mums feeding their pups inside.
Our success wasn’t lost on other bat workers, and at least five more big bat houses are being built. Many more will follow.
BCI members can read the whole story on the new Dutch bat houses in the Fall 2006 issue of BATS magazine.