Download Mixed-species primate associations are known that two or more

Mixed-species association is a phenomenon that members of two or more species move and
forage together like one species. Various primate species living in Africa and South America,
including red-tailed monkeys (Cercopithecus ascanius) and blue monkeys (C. mitis), are reported to
make mixed-species associations. A variety of functions (e.g. anti-predator behavior, effective
foraging, etc.) have been proposed for such associations. Cords（1987）reported that red-tailed and
blue monkeys made associations for the anti-raptor predators in the Kakamega Forest, Kenya. In
the Kalinzu forest of Uganda, however, predators on these two species are not only raptors but also
chimpanzees.
To examine whether red-tailed and blue monkeys make associations to avoid predations by
chimpanzees, I studied how members of the associations respond to approaches by chimpanzees in
the Kalinzu forest.
Red-tailed and blue monkeys were both strictly arboreal in this study site.
A
target troop of red-tailed monkeys (R1 group) had 23 individuals and its home range size was about
26ha, while a target troop of blue monkeys (B1 group) had 24 individuals and its range was about 25
ha. The overlap of the two troops was very large.
We collected data on the movement pattern,
distance and vocalization of the two Cercopithecus species by following troops of each species
simultaneously.
Alarm calls against chimpanzees were emitted by females, but not by males. When a male
chimpanzee approached a mixed association, members of both species emitted always alarm calls. In
contrast, monkeys did not give alarm calls to groups of female chimpanzees and/or juveniles.
Distances between chimpanzees and monkeys had no correaltion with the occurrence of alarm calls.
These findings suggest that red-tailed and blue monkeys may evaluate the risk of predation
according to the sex/age class of chimpanzees.