52 - Modeling Risk with Locomotor Behavior in Chimpanzees

Poster Board Number: 52
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Abstract Body : Locomotor risk is inherent to all animals. This is especially true for arboreal species, who must move between different canopy levels. Chimpanzees, Pan troglogytes, are terrestrial travelers and arboreal feeders, repeatedly needing to climb in and out of the canopy and traverse discontinuous pathways. In this study, we investigate locomotor risk among the chimpanzees of the Ngogo communities in Kibale Forest, Uganda to ultimately understand what variables are predictive of risk in humans’ closest living relatives. We hypothesize that: 1) age is a significant variable, with chimpanzee subadults, like humans, engaging in the highest level of risky behavior, 2) sex is not a significant predictor of risk, and 3) higher heights (above 10 minutes) are less associated with risky behaviors than lower heights due to the increased chance of injury from falling. We filmed chimpanzees in 4K 60fps ad libitum during descent and coded the videos for individual ID, age class, sex, locomotor mode, and height. We used the occurrence of leap and drop, where there is sustained free flight, to quantify risk using a generalized linear mixed model. We found that age class had a significant effect on risky behavior, with infants, juveniles, and adolescents all riskier than adults. Neither sex nor height were significant predictors of risk. These results support the hypotheses that subadults engage in riskier behavior than adults and that there is no difference between males and females. Despite the greater cost of falling from increased heights, our third hypothesis was not supported. These findings are the first analysis of locomotor risk in wild chimpanzees, an ideal species for researching age-related differences in these behaviors. This study has implications for understanding human locomotor risk as a similar age examination is not feasible due to adult locomotor supervision of subadults on difficult terrain.