1. Evolution and Social Interaction Research Group, Nottingham Trent University, Nottingham NG1 4FQ, UK
2. Centre for Comparative and Evolutionary Psychology, University of Portsmouth, Portsmouth PO1 2UP, UK
3. Macaca Nigra Project, Tangkoko-Batuangus Nature Reserve, North Sulawesi, Indonesia
4. Faculty of Veterinary Medicine, Agricultural University of Bogor, Bogor, Jawa Barat 16680, Indonesia