Red-tailed monkeys (Cercopithecus ascanius) prey upon and mob birds in the Issa Valley, western Tanzania.

Interactions between monkeys and birds are rarely observed and, consequently, rarely described in the scientific literature. We recorded two encounters between birds (Prionops plumatus and Strix woodfordii) and red-tailed monkeys (Cercopithecus ascanius) in a woodland-mosaic habitat in western Tanzania. We observed a male red-tailed monkey consume a small bird in its entirety. Although only a few feathers remained, we provisionally identified the bird as a white-crested helmetshrike. We also observed a group of red-tailed monkeys mobbing, but not killing, an African wood owl on the forest floor. This is the first reported observation of this kind. These encounters suggest that guenons may generalize large-bodied avians as threats and small-bodied avians as potential prey. Hetero-specific encounters such as these provide insights into primate diet and anti-predatory behavior.