Flexible grouping patterns in a western and eastern chimpanzee community

Kathelijne Koops*, Walter Akankwasa, Henry Didier Camara, Maegan Fitzgerald, Alex Keir, Gnan Mamy, Tetsuro Matsuzawa, Hella Péter, Kizza Vicent, Klaus Zuberbühler, Catherine Hobaiter*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Primate social organizations, or grouping patterns, vary significantly across species. Behavioral strategies that allow for flexibility in grouping patterns offer a means to reduce the costs of group living. Chimpanzees (Pan troglodytes) have a fission-fusion social system in which temporary subgroups (“parties”) change in composition because of local socio-ecological conditions. Notably, western chimpanzees (P. t. verus) are described as showing a higher degree of bisexual bonding and association than eastern chimpanzees, and eastern female chimpanzees (P. t. schweinfurthii) are thought to be more solitary than western female chimpanzees. However, reported comparisons in sociality currently depend on a small number of study groups, particularly in western chimpanzees, and variation in methods. The inclusion of additional communities and direct comparison using the same methods are essential to assess whether reported subspecies differences in sociality hold in this behaviorally heterogeneous species. We explored whether sociality differs between two communities of chimpanzees using the same motion-triggered camera technology and definitions of social measures. We compare party size and composition (party type, sex ratio) between the western Gahtoy community in the Nimba Mountains (Guinea) and the eastern Waibira community in the Budongo Forest (Uganda). Once potential competition for resources such as food and mating opportunities were controlled for, subspecies did not substantially influence the number of individuals in a party. We found a higher sex-ratio, indicating more males in a party, in Waibira; this pattern was driven by a greater likelihood in Gahtoy to be in all-female parties. This finding is the opposite of what was expected for eastern chimpanzees, where female-only parties are predicted to be more common. Our results highlight the flexibility in chimpanzee sociality, and caution against subspecies level generalizations.
Original languageEnglish
Article numbere23593
JournalAmerican Journal of Primatology
VolumeEarly View
Early online date22 Jan 2024
DOIs
Publication statusE-pub ahead of print - 22 Jan 2024

Keywords

  • Sociality
  • Party composition
  • Party size
  • Camera trapping
  • Chimpanzee

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