Form and Function of Food-Associated Calling in the Rekambo Community of Chimpanzees (Pan troglodytes troglodytes) in Loango National Park, Gabon

Date

2023-09-28

Authors

Warshawski, Lindsey

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Abstract

An important question in human evolution is when, how, and why did our species develop language. While the gap between human and non-human communication is significant, the cognitive precursors of human language are argued to be rooted in our primate lineage. One of our closest living relatives, chimpanzees (Pan troglodytes), offers insight into which communicative capacities emerged before and after hominins diverged from the Pan lineage seven to eight million years ago. Chimpanzees possess several short- and long-distance vocalizations that serve a variety of social functions and are emitted in various contexts. Chimpanzee food-associated calls (FACs) are emitted in foraging contexts; however, these vocalizations are only produced for approximately half of all feeding events. Investigating the social and ecological contexts in which FACs are produced can shed light on the functions of these calls. This is in turn can help us understand what chimpanzees are conveying with their vocalizations. This thesis seeks to contribute to the variability in both form and function(s) observed in wild chimpanzees’ FACs. This research explores if the FACs of the Rekambo chimpanzee (Pan troglodytes troglodytes) community in Loango National Park, Gabon function to attract conspecifics to a food patch; if callers direct FACs toward nearby individuals; and, if FACs function to promote proximity between group members. How fundamental frequency (F0) (the lowest frequency of a given sound measured in hertz (Hz)) of FACs changes over the course of a feeding event is also examined. Lastly, whether FACs function referentially is investigated by testing differences in F0 in relation to food types. Results show that the focal was more likely to food call upon arriving to a feeding event where they fed for longer with at least one other individual, potentially prolonging inter-individual proximity between group members. The F0 of FACs decreased as calling progressed throughout a feeding event, with calls emitted earlier tending to have higher fundamental frequencies than those emitted later on. Overall, these findings support the notion that FACs are influenced by social contexts, and that acoustic variation correlates to arousal. These findings align with results shown in other wild chimpanzee communities, while also providing new insight regarding acoustic properties concerning arousal while feeding. Finally, this work also adds to the growing body of literature that the function(s) of chimpanzee food calls may vary across communities.

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Keywords

chimpanzee, animal communication, food-associated calls, language evolution, animal cognition, primate communication, Pan troglodytes, primate cognition

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