Inter-community behavioural variation confirmed through indirect methods in four neighbouring chimpanzee communities in Cantanhez NP, Guinea-Bissau

Abstract

Culture, while long viewed as exclusively human, has now been demonstrated across diverse taxa and contexts. However, most animal culture data are constrained to well-studied, habituated groups. This is the case for chimpanzees, arguably the most ‘cultural’ non-human species. While much progress has been made charting wild chimpanzees' cultural repertoire, large gaps remain in our knowledge of the majority of the continent's chimpanzees. Furthermore, few studies have compared neighbouring communities, despite such comparisons providing the strongest evidence for culture, and few have studied communities living in anthropogenic habitats although their culture is in imminent danger of disappearing. Here we combine direct, indirect and remote methods, including camera traps, to study, over 2 years, four unhabituated neighbouring chimpanzee communities inhabiting human-impacted habitats in Cantanhez NP, Guinea-Bissau. From traces collected during 1089 km of reconnaissance walks and 4197 videos from 56 camera trap locations, we identified 18 putative cultural traits. These included some noteworthy novel behaviours for these communities, and behaviours possibly new to the species. We created preliminary behavioural profiles for each community, and found inter-community differences spanning tool use, communication, and social behaviour, demonstrating the importance of comparing neighbouring communities and of studying previously neglected communities including those inhabiting anthropogenic landscapes.

Dialects in leaf-clipping and other leaf-modifying gestures between neighbouring communities of East African chimpanzees

“…Leaf-clipping is a non-vocal signal, used by chimpanzees and bonobos, that has been suggested as a potential cultural candidate, supported by the variation in its presence across communities 2 , 17 (Table 1 ), and by possible variation in its expression as well as the behavioural contexts in which is it used 2 , 18 – 22 . It has also been suggested as an example of gestural dialects in chimpanzees 23 .…”

“…It has also been suggested as an example of gestural dialects in chimpanzees 23 . While some researchers have described leaf-clipping as a type of tool use 18 , 19 , 22 , descriptions of a behaviour as tool-use or signal are not mutually exclusive 22 —an object used to produce a gesture may also be considered a communicative tool. Nonetheless, a systematic investigation of this behaviour between neighbouring communities living in the same forest environment and with regular gene flow has not yet been attempted (c.f.…”

“…Nonetheless, a systematic investigation of this behaviour between neighbouring communities living in the same forest environment and with regular gene flow has not yet been attempted (c.f. Bessa et al 18 for an initial description).…”

“…In this first published description, Nishida speculated that leaf-clipping may represent an example of ‘traditional drift’ 24 . Further discussions and descriptions of leaf-clipping developed this idea and considered the trait to be likely cultural due to apparent variation in use and expression between communities 2 , 18 , 19 . Across communities, this behaviour primarily occurs in sexual contexts and is argued to function as a courtship behaviour to solicit copulations, particularly by young males toward females in oestrus 19 , 22 , 24 ; however, it is also observed preceding buttress drumming 18 , 19 , 22 , 25 .…”

Innovative multi-material tool use in the pant-hoot display of a chimpanzee

“…This call type is deployed in a number of contexts for various functions including group coordination 35 , group movement 35 , strengthening social bonds 36 , feeding 5 , 35 – 37 and dominance displays 38 . During the production of these calls, wild individuals regularly combine their pant-hoot with behaviours that interact with the caller’s environment, such as drumming on the buttresses of trees 39 , dragging branches 40 and throwing rocks 41 . Although the function of interacting with these materials is little understood, a reasonable assumption is that they augment the vocal component of the signal—perhaps providing contextual information to receivers 42 , or simply increasing the saliency of the display 38 , 43 , 44 .…”