Risk-taking in samango monkeys

The risk an animal perceives can be measured using an experimental patch approach called giving-up densities (GUDs). GUDs can be used to explore the “Risk-Disturbance Hypothesis” (RDH) which stipulates that risk from humans parallels risk from natural predators in its effects on animals’ foraging and habitat use. We studied arboreal samango monkeys (Cercopithecus mitis sspp.) at two sites with varying predation and anthropogenic pressures: Lajuma, a research site in western Soutpansberg Mountains and Hogsback, a village-forest matrix in the Amathole Mountains. We found pronounced effects of human observers and human-modified areas on monkeys’ GUDs. The impact of humans did not simplistically follow predictions from the RDH. At Lajuma, monkeys exploited high-risk (ground-level) patches more intensively in the presence of researchers, likely perceived as shields against terrestrial predators. Meanwhile, at Hogsback (predator-poor site), where monkeys forage on exotic seeds in people’s gardens, especially in winter, monkeys showed a preference for indigenous forest given equal feeding opportunities in gardens and forest. Monkeys were quick to exploit newly available food sources, and distinguish between risks.