Chelluri, G. I., Ross, S. R., Wagner, K. E. 2013. Behavioral correlates and welfare implications of informal interactions between caretakers and zoo-housed chimpanzees and gorillas. Applied Animal Behaviour Science 147, 306-315.

In captive animal facilities, human staff members are a relevant part of the animals’ social environment in addition to providing care and managing the social group. Structured, predictable interactions and relaxed, spontaneous contacts may all affect the animals’ behavior and well-being, both immediately and in the long term. This study examined the association between unstructured, affiliative caretaker–animal interactions and the behavior of zoo-housed chimpanzees (Pan troglodytes) and Western lowland gorillas (Gorilla gorilla gorilla). The interactions in question included play, spontaneous feeding, and other positive vocal and visual interactions performed through a protective mesh barrier. Behavioral data collected over 48 months were used to identify correlates of caretaker interactions among key behaviors relevant to welfare assessment, including agonism, sexual behavior, abnormal behavior, prosocial behavior, and self-directed behavior, as well as the presence of wounds. In observational sessions containing one or more caretaker interactions, chimpanzees and gorillas both showed higher agonism (P = 0.044 and P = 0.042, respectively) and lower self-directed behavior (P = 0.035 for chimpanzees and P = 0.001 for gorillas) than in control samples. Agonism rose in chimpanzees from an average of 0.01–0.12% of overall behaviors, and in gorillas from 0% to 0.1%, while self-directed behavior decreased in chimpanzees from an average of 9.54–7.81% and in gorillas from 11.02% to 7.38%. Chimpanzees also showed lower intraspecific prosocial behavior in samples with caretaker interactions (P = 0.044), decreasing from an average of 11.5% to 5.52% of overall behaviors. Finally, gorillas exhibited less abnormal behavior in caretaker interaction samples than in control samples (P = 0.029), decreasing from a mean of 2.42–1.77% of overall behaviors. In chimpanzees, higher agonism and lower prosocial behavior are indicative of greater arousal, although we would expect self-directed behavior to rise rather than decrease in that situation. The results in gorillas are mixed with respect to welfare outcomes: higher agonism is indicative of arousal, but lower abnormal and self-directed behaviors suggest a decrease in stress and anxiety. These findings underscore the importance of understanding the influence of all forms of interaction with heterospecifics and demonstrate a need for welfare assessments that include even positively intended interactions.

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