1. Institute for Forestry and Nature Research, P.O. Box 23, NL‐6700 AA Wageningen, The Netherlands
2. Agricultural University, Department of Terrestrial Ecology and Nature Conservation, P.O. Box 338, NL‐6700 AH Wageningen, The Netherlands
3. Netherlands Bat Research Foundation, Lutherse Burgwal 24, NL‐2512 CB 's Gravenhage, The Netherlands