Evaluating the co-occurrence of abnormal behaviors in chimpanzees (Pan troglodytes) (2025)

Whitham, J. C., Hall, K., Miller, L. J.

Abstract

For decades, welfare scientists have focused on investigating and mitigating the abnormal behaviors—including repetitive stereotypic behaviors and abnormal stances/postures—displayed by chimpanzees residing in professionally managed settings. In an effort to design feasible and practical welfare assessments, researchers often pool abnormal behaviors into subcategories. However, this approach can result in the creation of heterogeneous subcategories comprised of behaviors that do not statistically co-occur. This study examined the co-occurrence of abnormal behaviors in 41 adult chimpanzees living in 16 facilities accredited by Association of Zoos and Aquariums. Specifically, we employed principal component analysis and regression analyses to investigate the following behaviors: self-directed hair pluck, idiosyncratic body manipulations (e.g., eye-poking), and idiosyncratic movements/postures (e.g., rocking). We found: (1) none of the behaviors loaded onto the same component, and (2) no significant relationships were discovered by performing the regression analyses. These findings suggest that self-directed hair pluck, idiosyncratic body manipulations, and idiosyncratic movements/postures are heterogeneous and should be scored separately in future studies of adult chimpanzees. Though this study cannot provide insight into the potential triggers for these specific behaviors, the lack of positive associations suggests that they may have unrelated triggers and treatments. Ultimately, future research should attempt to reduce and eliminate abnormal behaviors by introducing tailored interventions to the husbandry routine and/or environment. The findings of this study can be extended to other taxa. Specifically, welfare researchers should analyze individual abnormal behaviors separately, instead of forming subcategories of abnormal behaviors, unless behaviors are found to statistically co-occur.