Frequent predation on primates by crowned eagles (Stephanoaetus coronatus) in Mahale Mountains National Park, Tanzania.

The significance of raptor predation has been repeatedly emphasized in studies on arboreal primates; however, there are few studies on the predation of primates by raptors in primate-rich forest environments. Among the raptor species, the crowned eagle in Africa is known to be a primate-predator. In this study, a video camera was set up at the nesting site of a crowned eagle pair in the Mahale Mountains National Park in Tanzania, and the prey species delivered to the nest by the pair were identified by analyzing the video footage. Of the 46 prey deliveries recorded during 4.5 months of recording in the nestling season, primates accounted for 26 cases, of which 16 were red-tailed monkeys, the most abundant primates in the area. No prey was clearly identified as red colobus, despite a seemingly high density of this monkey species. This result suggests that predation by the eagles was biased toward the red-tailed monkey in Mahale, whereas no such bias toward the same monkey species was reported in a previous study conducted in Kibale. Furthermore, among different predator species in Mahale, only the crowned eagle prey primarily on red-tailed monkeys. Although chimpanzees and leopards inhabiting the study area are also significant predators of monkeys, these two species prefer red colobus to red-tailed monkeys. This suggests that these two monkey species living in the same forest have different primary predatory threats.