1 RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, Edinburgh, EH12 9DH, UK. graeme.buchanan@rspb.org.uk.
2 RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, Edinburgh, EH12 9DH, UK.
3 Wildlife Biology Program, Department of Ecosystem and Conservation Sciences, W.A. Franke College of Forestry and Conservation, University of Montana, Missoula, MT 59812, USA.
4 Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Bogotá, DC, 11122, Colombia.
5 Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch 7602, South Africa.