Assessing chimpanzees’ fluency of movement: Applications for monitoring health and welfare

With age, primates’ activity levels and ease of movement may decline and changes in locomotory behaviour may reflect changes in health. Thus, developing quick and reliable measures of movement has important applications for measuring recovery from disease, injury, or any age-related mobility declines. While behavioural observations can offer a rich understanding of primates’ activity budgets and rates of locomotory behaviours, such data are often time consuming to collect, require trained personnel, and may not capture aspects of primates’ movement that relate to welfare, such as fluency of movement. Here, we assessed the reliability and utility of a published chimpanzee mobility rating scale (Mobility Scoring System) with a new population of sanctuary-housed chimpanzees. We also developed a novel movement measure: the Fluency Scoring Scale. The Mobility Scoring System is comprised of six questions that staff can use to rate individual chimpanzee's mobility. The Fluency Score Scale is used in conjunction with behavioural observations to rate the fluency with which a chimpanzee performs locomotory behaviour. We studied 30 chimpanzees at Chimp Haven with no known disease or injury that would impact their movement in order to assess typical mobility by age. By studying individuals aged 21–53 years old, we assessed if chimpanzees’ mobility scores (as rated by care staff using the Mobility Scoring System) and movement fluency scores (as scored independently by an observer collecting observational data) correlated with age as well as rates of locomotory behaviour. The raters showed strong agreement in their scores for all six mobility measures, both in the pre- and post-study phases. We found that the chimpanzees’ mobility scores and movement fluency scores were significantly correlated with age, such that older individuals had poorer mobility and movement fluency. We also found that the chimpanzees’ mobility scores were correlated with their movement fluency scores. However, we did not find that either the mobility scores nor movement fluency scores correlated with chimpanzees’ rates of locomotory behaviour. Furthermore, we did not find that older chimpanzees performed less locomotory behaviour than younger individuals. Thus, the Mobility Scoring System and Fluency Scoring Scale appear to capture chimpanzees’ ease of movement rather than rates of movement. Such mobility metrics may be of use to managers seeking to evaluate enclosure suitability for aging chimpanzees and future work should assess how well these scales can capture changes in mobility over time and their sensitivity to measuring the movement of chimpanzees with known mobility impairments.