About the Authors

Stephen R. Ross

sross@lpzoo.org

Affiliation Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America

Vivian M. Vreeman

Affiliation Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America

Elizabeth V. Lonsdorf

Affiliations Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America, Committee on Evolutionary Biology, University of Chicago, Chicago, Illinois, United States of America

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: SR EL VV. Performed the experiments: SR VV. Analyzed the data: SR VV EL. Contributed reagents/materials/analysis tools: SR EL. Wrote the paper: SR EL VV.