1. Catalan Ornithological Institute, ES-08019 Barcelona, Spain
2. InForest Joint Research Unit (CTFC-CREAF), ES-25280 Solsona, Spain
3. Centre of Ecological Research and Forestry Applications, ES-08193 Bellaterra, Spain
4. Consejo Superior de Investigaciones Científicas, ES-08193 Cerdanyola del Vallès, Spain