In 1995 Gunter Hartz and Ulrich Marckmann, former members of the local group of the NGO Nabu, built about 100 bat boxes and received another 100 bat boxes from the city of Kiel, which they then distributed around likely bat habitats. Every fall since then these boxes have been checked and cleaned and data about the bats is being collected.
An overview of the first five years shows that bat boxes may already be used after a very short time. They are also popular with birds, who seem to also suffer from housing problems, and hornets and wasps, which will often find that bat boxes are too small for them after a while.
In our experience checking all 200 boxes requires about four weekends and a number of helpers as 200 trees have to be climbed, boxes opened carefully first checking for hornets or – worse – wasps. The boxes need to be cleaned and any bats encountered need to be checked for species and markings.
Species include (at the time of the cleaning) Nyctalus noctula, Pipistrellus nathusii, Pipistrellus pipistrellus and Pipistrellus pygmaeus. As one (and only one) Myotis natteri has been found regularly during the past years in boxes close to one another this may be the same animal every year.