What preys on redtail monkeys?

Though actually seeing a redtail monkey attacked by a predator is EXTREMELY rare, the threat is obvious given how redtails respond to certain animals.

Last week, one of the field assistants spotted the remains of a redtail monkey attacked and eaten by a predator. It's hard to tell what killed the individual because all that remained were tufts of unmistakably redtail hair, a mandible, and some fragments of long bones. The third molars were still emerging, indicating that the victim was not fully adult yet.

Redtails' main predators are eagles and chimpanzees. Most days in the field, I hear blue monkeys and redtail monkeys alarm calling in tandem when eagles fly overhead or if eagles are calling nearby. Redtails also tend to have a stereotypical reaction to the presence of chimpanzees less than 50 meters away: become extremely quiet, run like hell, then sit silent, not feeding or socializing for at least 45 minutes. On days when multiple chimp subgroups are around, this sequence continues on repeat for several hours. Given this typical flee-and-hide reaction by redtails to chimps, the fact that a chimp researcher recently saw a young chimp gently groom an adult redtail is surprising (for video footage and discussion see University of New Mexico PhD student Kris Sabbi's blog post).