[1] Univ Cambridge, Dept Zool, Conservat Sci Grp, Cambridge CB2 3EJ, England
[2] Zool Soc London, Conservat Programmes, London NW1 4RY, England
[3] Zool Soc London, Inst Zool, London NW1 4RY, England
[4] Royal Soc Protect Birds, Sandy SG19 2DL, Beds, England
[5] UNEP World Conservat Monitoring Ctr, Cambridge CB3 0DL, England