1. Ministry of Education Key Laboratory for Biodiversity Sciences and Ecological Engineering, College of Life Sciences, Beijing Normal University , Beijing 100875 , China
2. Department of Ornithology, Max Planck Institute for Biological Intelligence , Seewiesen 82319 , Germany
3. Edward Grey Institute, Department of Zoology, University of Oxford , Oxford OX1 3PS , UK
4. Academy of Forestry Inventory and Planning, National Forestry and Grassland Administration , Dongcheng District, Hepinglidongjie No. 18, Beijing 100714 , China and
5. School of Ecology and Nature Conservation, Beijing Forestry University , Beijing 100083 , China