1. Conservation Ecology Group, Department of Biosciences, Durham University, South Road, Durham, DH1 3LE, UK
2. Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, SL5 7PY, UK
3. School of Biology, University of St Andrews, St Andrews, Fife KY16 9ST, UK
4. BirdLife International, David Attenborough Building, Pembroke St., Cambridge, CB2 3QZ, UK
5. Department of Zoology, University of Cambridge, Downing St, Cambridge, CB2 3EJ, UK