Researchers conducted a three-year study of two neighbouring chimpanzee groups in Côte d’Ivoire, tracking the primates as they traversed their respective territories, including an overlapping border area where skirmishes occasionally took place. The team found that chimpanzees were more than twice as likely to climb hills when heading towards this contested frontier as when they were travelling into the heart of their own territory. The study was conducted at the Taï Chimpanzee Project (CNRS, France) and was initiated at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.