1. The Helsinki Lab of Ornithology (HelLO), Finnish Museum of Natural History, University of Helsinki, FI-00014 Helsinki, Finland
2. School for Forest Management, Swedish University of Agricultural Sciences (SLU), Box 43, SE-739 21 Skinnskatteberg, Sweden
3. Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden