About the Authors
School of Psychology, University of St Andrews, St Andrews, Scotland
Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
Department of Anthropology, Southern-Illinois University, Carbondale, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: KZ. Performed the experiments: EC. Analyzed the data: EC. Contributed reagents/materials/analysis tools: KZ UR. Wrote the paper: KZ EC. Other: Director of gibbon field site at Khao Yai, provided access to study site, habituated animals, provided permits and invaluable background information on the gibbons: UR.