Socio-communicative behaviors of West African chimpanzees (Pan troglodytes verus) in a savanna habitat at Fongoli, Senegal

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2021-08
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Rabinowitz, Andrea
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Pruetz, Jill D
Bronikowski, Anne
Nuñez, Cassandra
Toth, Amy
Shelley, Mack
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Ecology, Evolution, and Organismal Biology
Abstract
Researchers of many disciplines continue their pursuit to reconstruct the evolution of language, as it remains one of the few traits separating humans from other animal taxa. Because behavior does not leave evident traces in the fossil record, understanding the communication strategies of nonhuman primates, especially chimpanzees (Pan troglodytes), provides the opportunity to help expose language’s ancestral history. The first chapter presents a review discussing the history of chimpanzee communication research, highlighting the advanced social and cognitive traits shared with human language. Studying the socio-communicative behaviors of savanna chimpanzees inhabiting an environment similar to that in which ancient hominins evolved further informs our understanding of the selective pressures that affected communication in the last common ancestor that humans share with our closes primate relatives (LCA). Therefore, the second and third dissertation chapters are studies of the chimpanzees at the Fongoli site in Senegal, West Africa to document how they employed their communicative signals, with special attention paid to the influence of social factors. Here I present the signal repertoire of the Fongoli community, including vocal, gestural, and combined signals. The resulting observations reveal variation in repertoire size and signaling rate between individuals and age-sex classes, with adult males using more signals than other demographic groups, as well as producing vocal and combined signals at a higher rate. The most common signals in each demographic group also reflected their social roles within the community. This study additionally contributes to the recognized cultural diversity observed between chimpanzee populations, as Fongoli chimpanzees’ repertoire also varies from other study populations. In further analysis, I report that the adult males of the Fongoli chimpanzee community utilize multiple strategies to differentially express their social relationships including joint vocalizing. The joint pant-hoot call provides a means to maintain their social bonds that is less costly than allo-grooming, but is more selective than spatial proximity. Individual males also differ in their vocal and social behaviors, in ways that do not strictly align with their dominance hierarchy, indicating greater nuance with their social environment than expected. Overall, this dissertation offers insight to the communicative strategies of an ecologically and behaviorally important chimpanzee community, specifically how they differ regarding individual social relationships. I consequently emphasize the importance of diversifying study populations and recognizing the complexities involved in disentangling the many aspects of language origins.
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