Neighbors Matter: An Investigation into Intergroup Interactions Affecting the Social Networks of Adjacent Chimpanzee Groups

Abstract

Wild chimpanzees live in large and complex social communities, but their complexity is determined by the number of potential social partners as well as the frequent changes in group composition due to fission–fusion dynamics. Alternatively, captive housed chimpanzee groups are usually much smaller and less complex. However, studies have shown that groups can be housed in adjacent habitats, potentially increasing the number of social partners, i.e., granting additional relationship opportunities and enhanced social complexity. While most social network studies analyze social groups as closed systems, this study assessed the impact of social interactions between two neighboring groups of chimpanzees, based on two social network indices (Vertex strength centrality and Deviation from edge weight disparity). Furthermore, Linear Mixed Models (LMMs) were employed to assess whether gender, age, and intra-/intergroup directionality influenced these indices. We recorded occurrences of social behaviors, social proximity and whether chimpanzees observed individuals in the other group as a measure of interest. Most social behaviors were directed towards group members; however, 13% were directed towards the neighboring group. Although enclosure barriers constrained the chimpanzee’s capacity to physically interact, it does not necessarily impede social interactions with the outside world. Hence, the presence of neighboring chimpanzees potentially provides additional relationship opportunities, increasing social stimulation and complexity leading to an enriching social environment.

Neighbors, Pros and Cons: Impact of Intergroup Interactions on the Welfare of Captive Chimpanzee Groups (Pan troglodytes)

“…As already hypothesized in our previous article [57], we now provide more findings supporting the original argument that the adjacent housing of different chimpanzee groups has the potential to provide additional social relationship opportunities, i.e., increased social complexity and stimulation passively due to the proximity and visual and auditory contact as well as directly through direct intergroup interactions. However, we strongly desire to emphasize that while this could be understood as a purely welfare-promoting factor, an increase in social stimulation and complexity and, to a certain degree, forced proximity may potentially also produce undesired impacts, such as augmented stress levels and increases in inter-and/or intra-conflicts, which need to be continuously evaluated and monitored.…”

“…Other studies on chimpanzees demonstrated how auditory information, such as, for example, hearing other chimpanzees socially interacting from physically and visually separated groups, produced a contagious effect on the social dynamics of adjacently housed individuals [56]. Gil-Dolz and colleagues [57] reported that interactions between two physically separated groups of chimpanzees housed in adjoining habitats occurred frequently enough that they were considered to be in the animals' social networks, thus producing an augmentation of the complexity of their social networks. However, to our knowledge, so far no information has been published on how such interactions between groups may impact the chimpanzees' behavior and, in continuation, their well-being in captivity.…”

“…Thus, the main objective of the present study is to follow up on the previously mentioned study conducted by Gill-Dolz and colleagues [57] to assess how interactions between two captive groups of chimpanzees housed in adjoining habitats influence the individuals' behavior and social dynamics within each group. Specifically, we are expecting to find that (1) agonistic intergroup interactions will produce an increase in self-directed and abnormal behaviors; (2) agonistic intergroup interactions will produce an increase in agonistic inter-and intragroup interactions; (3) agonistic intergroup interactions will increase the frequency of affiliative interactions between members of the same group; and (4) affiliative intergroup interactions will have a neutral impact on or produce an increase in the affiliative interactions between group members.…”

Sign Language Studies with Chimpanzees in Sanctuary

“…This indicates sociality between separate social groups in captivity. This supports other research that shows interactions between neighboring groups of captive chimpanzees can be a source of social stimulation [46][47][48]. The logs provide some insight into the nature of introductions between chimpanzees and their perceptions of the individuals around them.…”