Male blue monkey alarm calls encode predator type and distance

There is considerable controversy about what is encoded when primates produce alarm calls to an external event. Results are often compatible with multiple explanations, such as differences in a callerʹs perceived level of threat, direction of attack or category of predator. Using acoustic predator models, we investigated how male blue monkeysʹ, Cercopithecus mitis stuhlmani, alarm calls were affected by predator type, distance, and elevation. We found that individuals produced two types of acoustically distinct alarm calls, ‘pyows’ and ‘hacks’. Males produced these calls in predator-specific ways, but call rates were also affected by the distance and location of the predator. We discuss these findings in relation to the different predator hunting techniques and two common antipredator strategies pursued by monkeys, predator deterrence and conspecific warning.