About the Authors

Esther Clarke, Klaus Zuberbühler
School of Psychology, University of St Andrews, St Andrews, Scotland

Ulrich H. Reichard
Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

Ulrich H. Reichard
Department of Anthropology, Southern-Illinois University, Carbondale, United States of America

Corresponding Author

kz3@st-and.ac.uk

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

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.