Funding for this research was provided by:
Wenner-Gren Foundation (8784)
Alexander von Humboldt-Stiftung (DEU/1069105)
unspecified valid from 2016-02-01
Received: 3 July 2015
Revised: 23 November 2015
Accepted: 11 December 2015
First Online: 1 February 2016
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: All applicable international, national and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the chimpanzee projects at which the studies were conducted.