Fluid social systems place unique cognitive demands on individuals given the necessity to coordinate reunions and negotiate relationships over large distances and with intermittent encounters. A variety of fission-fusion species produce loud calls, a behavior likely critical in maintaining contact between widely spaced community members. Despite investigation into the variables that influence vocal behavior, previous research has been unable to situate interparty calling in a socio-ecological context, especially when callers are separated by large distances. This study will address the function of chimpanzee loud calls (pant hoots), as well as explore hypotheses concerning chimpanzee acoustic behavior and its relationship to the environment, important especially when using savanna chimpanzees to model early hominin behavioral adaptations to arid habitats. Specific objectives include examination of whether chimpanzees (1) use loud calls to coordinate reunions or movements between widely separated parties (enabling a large percentage of the community to maintain contact for prolonged periods of time), (2) exhibit specific sleeping-site calling behavior, and (3) adjust grouping patterns to scarce resources and/or predator density. To meet these objectives, an acoustic localization system has been developed that will monitor and record calling behavior and caller locations within (potentially) an entire chimpanzee community in Ugalla, Western Tanzania, providing data on fission-fusion patterns. Microphone units deployed across the study area will transmit, in real time, sounds to a central computer where data will be analyzed, stored, and used to locate chimpanzee parties for behavioural data collection. Spatial and regression analyses will assess the relationship between chimpanzee nesting sites and the acoustic environment, whilst streaming spectrographic software will be used to analyze pant hoots in various contexts.
For chimpanzees, where relative party size and recruitment of allies are key factors in intergroup (e.g. lethal raiding) and intragroup relations, vocalization behaviour is an important means through which individuals monitor each other's locations and behaviour, especially when not in visual contact. The extremely large home ranges of savanna chimpanzees (>270km2 compared to <15km2 in forests) are likely to impact the nature of parties, how they coordinate movement, and possibly on community social structure itself. Revealing how savanna chimpanzees maintain their social relationships in these conditions has implications for both Pliocene hominins that evolved in a similar habitat, and for the adaptability of a fission fusion system. More broadly, this study will develop and demonstrate a new technology that can be used for behavioral, ecological, and conservation research on any loudly vocalizing animal. Through training in the appropriate field and analytical methods, Tanzanian researchers and wildlife managers can then apply this new, useful technology to new additional research questions.
