1. Japan Bird Research Association, 1–29–9 Sumiyoshi, Fuchu, Tokyo 183–0034, Japan
2. Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 1–14 Bunkyo-machi, Nagasaki 852–8521, Japan
3. Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia
4. Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812–8581, Japan