From ridge tops to ravines: landscape drivers of chimpanzee ranging patterns

Abstract

Recent improvements in tracking technologies have resulted in a growing number of fine-scale animal movement studies in a variety of fields, from wildlife management to animal cognition. Most studies assume that an animal's ‘optimal’ foraging route is linear, ignoring the role the energy landscape can play in influencing movement efficiency. Our objective was to investigate whether landscape features that affect movement costs (topographical variation, superstrate and substrate) influence the movement of chimpanzees, Pan troglodytes, in a rugged, montane environment. We tested for route reuse and preferential use of human-made trails and ridge tops, using 14 months of focal follow data from 14 individuals and maps of established chimpanzee trails. Chimpanzees travelled on human-made trails significantly more than expected and showed weak preference for use of ridge tops for travel. Line density analysis demonstrated route reuse in chimpanzees and uncovered a network of high-use routes across their range. To our knowledge, this is the first study to empirically demonstrate route reuse and preferential use of human-made trails for travel by chimpanzees. We discuss the energetic and cognitive benefits of trail use and the implications for chimpanzee sociality. By applying resource selection and line density analysis to fine-scale movement data, this study demonstrates the importance of incorporating landscape features in predictive animal movement models.