1. Department of Biological Anthropology, Downing St., Cambridge CB2 3DZ and Sub‐Department of Animal Behaviour, High St., Madingley, Cambridge CB3 8AA
2. Large Animal Research Group, Storey's Way, Cambridge, CB3 ODT and Department de Biologia, U.P. Cayetano Heredia, Lima, Peru
3. Macaulay Land Use Research Institute, Pentlandfield, Roslin, Midlothian, Scotland EH25 9RF