Bat houses are rare in Norway, but several bat species frequently move into houses and other buildings, often generating unfortunate and misleading publicity about bats. The most common species found in buildings are northern bats (Eptesicus nilssonii) and soprano pipistrelles (Pipistrellus pygmaeus), both very small bats.
Officials usually recommend that homeowners wait until October, when bats have moved out, then refurbish the exterior to prevent the bats from returning in the spring. This can be useful advice, but it can also send the now-homeless bats into the house of a neighbor or leave them to die.
Tore Christian Michaelsen and Karl Johan Grimstad of the Norwegian Zoological Society used a grant from Bat Conservation International’s Global Grassroots Conservation Fund for a pilot project designed to resolve this problem. They wanted to determine whether bats will choose properly designed bat houses over human buildings and which species will use the bat houses.
This pioneering Global Grassroots project was made possible by donations from Mrs. Leon C. Hauser, The Hulebak-Rodricks Foundation, Ruth Gallagher and Noeline Gannaway.
The Zoological Society followed most BCI criteria in building the bat houses, but with several modifications to suit Norway’s cold climate and generally small bats. Because the most common bats in Norway are smaller than most U.S. bats, the team decided to limit roosting chambers to a maximum depth of three-quarters of an inch, and narrowed that even more for mounting on buildings used by the tiny soprano pipistrelles.
All the bat boxes were painted black for maximum warmth. Since the houses all allowed bats to move between two or three chambers, they discounted the threat of overheating and decided not to include air vents on the boxes.
The team built and mounted eight bat-boxes on homes and buildings in spring 2006. All but one were occupied by bats. More than 40 northern bats moved into one bat house, leaving only 10 bats in the building on which the bat box was mounted. The box had an experimental artificial heating unit installed in one of the chambers, but the bats seemed to prefer other parts of the box. No attempts were made to exclude the bats from this building – they just preferred the box.
The other six occupied bat houses each hosted a few soprano pipistrelles during our visits, but, based on the accumulation of guano, at least two of them had been used by a significant number during summer.
The Norwegian modifications to the standard BCI bat-house criteria seem to work well in this specific climate, and the results of the pilot study are certainly promising. The project has drawn such positive attention that Michaelsen and Grimstad say additional funding from local sources is now assured, and the project will continue.
You can help BCI’s Global Grassroots Conservation Fund support pioneering bat-conservation project around the world. Please contact our Department of Development: email@example.com.