Extent of threat detection depends on predator type and behavioral context in wild samango monkey groups

Abstract

Detecting predators requires information, and many behavioral and environmental features are predicted to enhance or limit an animal’s ability to learn about potential danger. Animals living in groups are thought to be at an advantage for learning about predator presence, but individual safety also depends on cues spreading from detectors to nondetectors as unsuspecting individuals may still be vulnerable. In this study, we simulated predator presence among two groups of wild samango monkeys (Cercopithecus albogularis schwarzi) to mimic natural encounters where only some individuals within a primate social group have access to personal information about potential threats. We did this using visual models of natural predators placed in positions for the monkeys to encounter within the landscape for a limited amount of time. We measured the number of individuals that were observed to detect and respond to these models with antipredator reactions, relative to subgroup size. While initial detectors that were able to spot the model themselves always reacted with overt behaviors such as alarm calling or staring at the model, responses did not typically spread to all group members. The number of initial detectors was also only weakly associated with the number of individuals that responded at the end of a trial. Initial responses to leopards were much stronger and more likely to spread than those given in response to pythons or eagles, and the importance of behaviors assumed to have an antipredator function depended on the type of predator the samangos encountered. Early detection is critical for prey to survive an encounter with an ambush predator. Social prey have the advantage of being able to rely on cues from conspecifics, though individuals that do not detect a potential threat can still be susceptible to attack. Here, we exposed wild samango monkeys to predator models to simulate predator presence to only part of a social group. Habitat visibility was a key predictor affecting collective detection, but the importance of other hypothesized factors—scanning and group spatial cohesion—depended on the predator species. Overall, our results indicate that the social effectiveness of purported risk-sensitive strategies varies based on the type of threat encountered.