[1] Graduate School of Agriculture, Hokkaido University, N9, W9, Sapporo,060-8589, Japan
[2] Department of Civil and Environmental Engineering, Faculty of Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami,UT,090-8507, Japan
[3] Faculty of Environmental Earth Science, Hokkaido University, N10, W5, Sapporo,060-0810, Japan
[4] Department of Agriculture and Animal Science, Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen 11, Inadacho,Obihiro,080-8555, Japan
[5] Nature Conservation Division, Chiba Prefectural Government, 1-1 Ichiba-cho, Chuo-ku,Chiba,260-8667, Japan
[6] Department of Biology, The University of North Carolina at Greensboro, 321 McIver Street, 312 Eberhart, Greensboro,NC,27412, United States
[7] Hokkaido Research Center, Forestry and Forest Products Research Institute, Hitsujigaoka 7, Sapporo,062-8516, Japan
[8] Konno Bird Research Center, 1−14, Nishi 15 Minami 37, Obihiro,080−0025, Japan