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Research on primates’ aptitude for navigating fine, compliant, and oblique branches has often focused on their postcranial morphology and locomotor mechanics. Here we aim to understand how primates perceive risk and make informed judgments to move safely. We video-recorded and digitized the locomotion of four lemur species (Ranomafana National Park) and 3 cercopithecoid monkeys (Kibale National Park). We test the general hypothesis that primates should change their gaits and engage in exploratory behaviors – using touch and sight as guides – to increase stability in precarious settings. Augmenting our prior study showing that some lemurs change their locomotion when moving high in the canopy, we present new data on the behavior of wild lemurs and monkeys as they cross gaps between substrates or switch between locomotor modes. They frequently cross gaps and transition between modes without pause, meaning they can accurately gauge their locomotor capacity before moving onto a new substrate. In an investigation on four species of captive lemurs (Duke Lemur Center), we examine how variations in substrate diameter, orientation, and compliance influence the paths lemurs choose to take. Preliminary results suggest that lemurs will tend to avoid the most precarious substrates in their paths, and future analysis will examine the role that light availability plays as well. Overall, this research highlights the importance of risk perception for robust locomotor performance while moving in arboreal environments. 

Much research on primate locomotor performance in arboreal settings focuses on how primate morphology allows them to navigate substrates that vary in diameter, orientation, and compliance. However, little prior research has considered how these and other environmental factors - such as substrate height and light availability - may also affect locomotor behavior by altering how risky a given substrate is perceived to be. To investigate the relationship between risk perception and locomotor performance, we video-recorded four species of wild lemur (Ranomafana National Park), three species of wild cercopithecoid monkeys (Kibale National Park), and four species of captive lemur (Duke Lemur Center). We test the general hypothesis that primates should change their gaits and engage in exploratory behaviors – using touch and sight as guides – to increase stability in precarious settings. Augmenting our prior study showing that some lemurs change their locomotion when moving high in the canopy, we present new data showing that wild lemurs and monkeys frequently cross gaps between substrates and transition between locomotor modes without pause. In the investigation on captive lemurs, we examine whether variations in branch diameter, compliance, orientation, and light availability influence the paths lemurs choose to take. Preliminary results suggest that lemurs tend to avoid the most precarious substrates (i.e., the most narrow and compliant) regardless of lighting conditions. Overall, this research indicates that primates are able to make quick and accurate judgements about locomotor safety in the context of ongoing arboreal locomotion.