• Between-task consistency, temporal stability and the role of posture in simple reach and fishing hand preference in chimpanzees (Pan troglodytes)

      Diaz, Sergio; Murray, Lindsay; Roberts, Sam; Rodway, Paul; Universidad Autónoma de Madrid; University of Chester: Liverpool John Moores University (Elsevier, 2021-07-31)
      Studying hand preferences in chimpanzees can provide insights into the evolutionary origins of human hemispheric specialization. Research on chimpanzee hand preference requires careful examination of important factors such as posture, between-task consistency and temporal stability, although few studies have investigated all of these factors in combination. We investigated hand preference in simple reach and fishing behaviours in a group of 19 chimpanzees at Chester Zoo in the UK. Simple reach was defined as extending a hand to grasp a small object, then flexing the limb in a continuous motion, and was examined in quadrupedal, sitting and climbing postures. Fish in hole was defined as inserting a stick into a hole in the wall with one hand and then extracting it with the same hand. Between-task consistency of hand preference was assessed by comparing simple reach and fish in hole, while temporal stability was assessed by comparing simple reach from two points in time: 2017 and 2019. The data showed no significant influence of posture on the strength of hand preference, which contrasts with previous research. The findings of this study show temporal stability in simple reach, although only partial between-task consistency. Overall, the results indicate that simple reach elicits laterality at the individual level and is consistent across postures and stable over time, which is consistent with the literature. These results suggest that posture stability may be important in affecting hand preference. Further, whilst there was overall stability in hand preference across time periods, some individuals changed their preferred hand, suggesting there may be individual level temporal instability of hand preference for certain tasks.
    • Social network analysis of a chimpanzee (Pan troglodytes) group in captivity following the integration of a new adult member

      Diaz, Sergio; Murray, Lindsay Elaine; Roberts, Sam; Rodway, Paul; University of Chester; Liverpool John Moores University
      Management of primates in captivity often presents the challenge of introducing new individuals into a group, and research investigating the stability of the social network in the medium-term after the introduction can help inform management decisions. We investigated the behavior of a group of chimpanzees (Pan troglodytes) housed at Chester Zoo, UK over 12 months (divided into three periods of four months) following the introduction of a new adult female. We recorded grooming, proximity, other affiliative behaviors and agonistic behaviors and used Social Network Analysis to investigate the stability, reciprocity and structure of the group, to examine the effect of rearing history on grooming network position and the role of sex in agonistic behavior. Both the grooming and agonistic networks correlated across all three periods, while affiliative networks correlated only between periods two and three. Males had significantly higher out-degree centrality in agonistic behaviors than females, indicating that they carried out agonistic behaviors more often than females. There was no significant difference in centrality between hand-reared and mother-reared chimpanzees. Overall, the group structure was stable and cohesive during the first year after the introduction of the new female, suggesting that this change did not destabilize the group. Our findings highlight the utility of Social Network Analysis in the study of primate sociality in captivity, and how it can be used to better understand primate behavior following the integration of new individuals.