Experimental evidence that titi and saki monkey alarm calls deter an ambush predator

Many animals use alarm calls in intraspecific communication to warn conspecifics of a predator's presence or to elicit coordinated group responses. However, alarm calls may also be aimed directly at the predator to discourage further pursuit. These 'pursuit-deterrent' signals are particularly important in the presence of ambush predators that rely on stealth to hunt prey. Here, we conducted playback experiments over a 16-month period on radiocollared ocelots, Leopardus pardalis, in Peru using audio stimuli of titi monkey (Callicebus toppini) and saki monkey (Pithecia rylandsi) alarm calls, with nonalarm loud calls as controls. We predicted that, if titi and saki alarm calls function as deterrent signals, then ocelots would move away from the sound source and leave the area following exposure to alarms but not following controls. We tracked ocelots via radiotelemetry for 30 min prior to and 30 min following experiments. At 15 min intervals we noted subject location, whether the cat was stationary or moving towards, away from or parallel to the playback area (calculated using a deflection angle) and distance travelled. Results showed a significantly different pattern in response movement between playback trials; ocelots moved away from the sound source in the majority of alarm trials but remained stationary/hidden or moved in a variety of directions following control trials. Ocelots also moved significantly farther following exposure to alarm trials than following exposure to controls. We conclude that ocelots can distinguish alarm calls from other loud calls and are deterred by alarm-calling monkeys. This is the first study to use playbacks on wild predators to test the pursuit-deterrent function of primate alarm calls.