1. School of Natural and Environmental Sciences; Newcastle University; Newcastle upon Tyne, NE1 7RU U.K.
2. School of Mathematical Sciences; Queensland University of Technology; 2 George St, Brisbane, QLD 4001 Australia
3. Conservation Science Group, Department of Zoology; Cambridge University, The David Attenborough Building; Cambridge, CB2 3QZ U.K.
4. US Geological Survey; Patuxent Wildlife Research Centre; 12100 Beech Forest Road, Laurel MD 20708 U.S.A.