In Norway, several bat species roost in homes and other buildings, and homeowner complaints periodically find their way into the news media. Although often based mostly on unnecessary fears and a lack of knowledge, these complaints nonetheless produce bad publicity for bats.
Local officials usually advise building owners to wait until late autumn, then refurbish the roof or other access points to prevent bats from returning. That can be good advice, but it can also be expensive. Plus, it leaves the bats in need of a new roost, which can simply transfer the problem to neighbors.
Tore Christian Michaelsen and Karl Johan Grimstad of the Norwegian Zoological Society, with a grant from BCI’s Global Grassroots Conservation Fund, set out to seek a solution. They initiated the first project using large-size bat houses in Norway. Most bat houses in the region have been very small compared to the typical bat house recommended by BCI for use in North America.
Michaelsen and Grimstad wanted to investigate whether the large bat boxes could be an alternative to refurbishing buildings to exclude bats and to document which bat species would use such boxes.
They used Bat Conservation International’s bat-house plans, but with several modifications to meet local conditions. Because some bat species expected to use the bat houses are quite small, they limited roosting chambers to no more than three-quarters of an inch (1.9 centimeters) wide, with some as small as two-thirds of an inch (1.6 centimeters).
By building boxes with two or three chambers, with provision for bats to move between chambers without leaving the box, they considered the problem of overheating in their northern climate to be insignificant. So they did not include air vents.
Of the eight bat houses installed during the first year, seven were occupied by bats. One housed a large colony of more than 40 northern bats (Eptesicus nilssonii). Only 10 bats continued to use the building on which the bat box was situated. No attempts were made to exclude the bats from this building – they just preferred the bat house.
The rest of the bat houses contained only small numbers of soprano pipistrelles (Pipistrellus pygmaeus) when the researchers visited them, but guano deposits beneath two of them indicated they had been used at some point by many bats.
The northern bat is the largest bat that commonly uses buildings as maternity roosts in Norway and these results show that the roosting space between bat-house partitions should be no more than three-quarters of an inch.
Michaelsen and Grimstad report that the results of their pilot study point strongly toward the increased use of large bat houses in Norway and also ensure enough funding to continue their research.
This Global Grassroots Conservation Fund grant was supported by The Hulebak-Rodricks Foundation, Mrs. Leon C. Houser, Ruth Gallagher and Noeline Gannaway.
You can help BCI support important bat-conservation programs like this one around the world through our Global Grassroots Conservation Fund. Please contact firstname.lastname@example.org.