Introduced mona monkey Cercopithecus mona is a key predator of bird nests in the endemic-rich Príncipe Island

Bird communities in oceanic islands tend to evolve under reduced predation, making them extremely susceptible to introduced predators. Príncipe Island (São Tomé and Príncipe, Central Africa) harbors 11 endemic bird species and eight introduced mammal species. To assess bird nest predation in Príncipe Natural Park, we deployed 55 artificial nests baited with quail eggs and monitored with camera traps. We recorded a 42% predation rate after 7 days. Out of 11 predation events recorded by camera traps, 10 were attributed to the introduced mona monkeys Cercopithecus mona. The likelihood of predation increased closer to communities, in higher nests, and in thinner trees. These remarkably high predation rates by an introduced species highlight the pressing need for a better understanding of how introduced species are affecting native biodiversity and ecosystem functioning on oceanic islands.