Locomotion as a Measure of Well-Being in Captive Chimpanzees (Pan troglodytes)

SIMPLE SUMMARY: Captive chimpanzee locomotion, including walking, climbing, brachiating, and hanging, is a species-typical behavior and increased locomotion is generally considered to indicate improved welfare. However, the relationship between locomotion and welfare is nuanced, and there is a limited number of studies that have used locomotion as a welfare indicator. We summarize findings from four previously published studies that showed increased locomotion in captive chimpanzees under social and physical environmental conditions is associated with enhanced welfare, including increases in space per animal and changes in the type of housing, housing in larger and more diverse groups, and during participation in an experimental medication choice paradigm. New data also showed that higher levels of locomotion are related to higher levels of behavioral diversity (an indicator of positive welfare), and lower levels of abnormal behavior and inactivity (behavioral indicators of negative welfare). Given this evidence, we suggest that time spent in locomotion can be used as a sensitive measure of welfare in captive chimpanzees. ABSTRACT: Locomotion in non-human primates, including walking, climbing, and brachiating among other types of movement (but not pacing), is a species-typical behavior that varies with age, social housing conditions, and environmental factors (e.g., season, food availability, physical housing conditions). Given that captive primates are typically observed to engage in lower levels of locomotor behaviors than their wild counterparts, increases in locomotion are generally considered to be indicative of improved welfare in captivity. However, increases in locomotion do not always occur with improvements in welfare, and sometimes occur under conditions of negative arousal. The use of time spent in locomotion as a welfare indicator in studies of well-being is relatively limited. We conducted focal animal observations on 120 captive chimpanzees across a series of studies and found higher percentages of time spent in locomotion (1) upon transfer to a new enclosure type, (2) in larger groups with wider within-group age ranges, and fewer males, and (3) with participation in an experimental medication choice paradigm. We also found that, among geriatric chimpanzees, those housed in nongeriatric groups exhibited more locomotion than those living in geriatric groups. Lastly, locomotion was significantly negatively correlated with several indicators of poor welfare and significantly positively correlated with behavioral diversity, one indicator of positive welfare. Overall, the increases in time spent in locomotion observed in these studies were part of an overall behavioral pattern indicative of enhanced welfare, suggesting that an increase in time spent in locomotion itself may be an indicator of enhanced welfare. As such, we suggest that levels of locomotion, which are typically assessed in most behavioral experiments, may be used more explicitly as indicators of welfare in chimpanzees.