Red-tailed monkeys (Cercopithecus ascanius) hunt green pigeons (Treron calva) in the Kalinzu Forest in Uganda

Red-tailed monkeys (Cercopithecus ascanius) were observed hunting green pigeons (Treron calva) in the Kalinzu Forest in Uganda. During 2 h 39 min, I observed two cases of successful hunting and one case of unsuccessful hunting in a Ficus saussureana tree. Red-tailed monkeys stalked the pigeons until they were within 2–3 m, and then jumped and caught them. In both successful cases, blue monkeys (C. mitis) ran to the hunting site from adjacent trees in order to poach the prey, and the red-tailed monkeys fled. One of these red-tailed monkeys dropped the pigeon while fleeing, and the blue monkey climbed down from the tree to search for it. This is the first record of cercopithecoid monkeys hunting birds that are outside of the nest and moving freely, and also the first record of red-tailed monkeys hunting vertebrates. However rare it may be, the repeated hunting attempts using similar techniques and the immediate attempt of blue monkeys to poach the prey suggest that this type of hunting was not a one-time event that happened by chance. Blue monkeys and an adult chimpanzee (Pan troglodytes schweinfurthii) in and around the fig tree did not attempt to hunt. The hunting of volant birds may be enabled by the small body size and the quick movements of red-tailed monkeys.