Recent encounters with rattlesnakes enhance ground squirrel responsiveness to predator cues

Abstract

A diverse range of prey taxa exhibit stereotyped antipredator behaviors when confronting live predators. Predator cues also elicit antipredator responses, and previous research indicates that prey possess mechanisms to discriminate between the relative risk posed by particular predator cues, which mediates their investment in antipredator behaviors (i.e., “threat-sensitive” behavior). However, the salience of such predator cues may change according to perceived predation risk, which can vary temporally or spatially. We hypothesized that prey modify responses to predatory cues according to their recent experience with predators, which would prime prey to attend to predator-related cues. In the present study, we found that recent encounters with live tethered rattlesnakes increased perceived predation risk in free-ranging California ground squirrels (Otospermophilus beecheyi), leading to concomitant increases in the intensity of antipredator behaviors displayed toward a predator model. The increase in antipredator behavior following snake encounters was higher toward the predator model than a novel object, suggesting that squirrels exhibit threat-sensitive responses toward objects resembling predators. However, squirrels did not treat either of these objects with caution, nor did they differ in antipredator behavior, when presented with the model or novel object when no live snake was encountered. This suggests that increased vigilance following predator encounters modulates responses to predator cues. Such increases in antipredator behavior could assist in detecting nearby predators quickly but could also have indirect effects on prey.

Underresponding to predators could lead to death, while overresponding could reduce time spent on other fitness-related activities. Prey balance these costs by using environmental cues to modify antipredator responses. Detecting a live predator in the environment could indicate that the chance of predation is high, which may enhance preys’ antipredator responses. We show that ground squirrels significantly enhance antipredator behaviors toward snake models and novel objects after encountering a live tethered rattlesnake predator. However, the predator model elicited greater antipredator behavior than the novel object following snake encounters, suggesting that squirrels are primed to attend to predator-related cues in this context. Both objects were treated similarly, and with less caution, when no snake was detected. Vigilance following predator interactions therefore mediates threat-sensitive responses to subsequent predator cues.