1. Department of Biology; University of York; York Yorkshire YO10 5DD UK
2. RSPB Centre for Conservation Science; Royal Society for the Protection of Birds, The Lodge; Sandy Bedfordshire SG19 2DL UK
3. RSPB Centre for Conservation Science; The David Attenborough Building Pembroke Street Cambridge CB2 3QZ UK
4. Conservation Science Group; Department of Zoology; University of Cambridge; Downing Street Cambridge CB2 3EJ UK