Funding for this research was provided by:
Deutscher Akademischer Austauschdienst
Max-Planck-Institut für Evolutionäre Anthropologie
Received: 28 February 2019
Revised: 12 July 2019
Accepted: 17 July 2019
First Online: 12 September 2019
Compliance with ethical standards
: The authors declare that they have no conflicts of interest.
: This study involved observation of animals in their natural habitat and was not disruptive to the subjects and the ecosystem. All observations were made from a 9 m high platform and animals were mostly unaware of the presence of the researchers. All study procedures complied with the national laws and regulations of the respective country, as well as the ethical standards of the Max Planck Institute for Evolutionary Anthropology and the Primatology department’s ethical guidelines for non-invasive research, and the Comité d’Ethique de la Recherche en Sciences de la Santé in Brazzaville, Republic of Congo.