The kinematic and behavioral components of the escape response can affect the outcomes of predator-prey interactions. For example, because sensory perception range can have spatial bias, and because turn duration before the initiation of escape locomotion can be smaller when prey is oriented away from predators, the prey's body orientation relative to a predator at the onset of the escape response (initial orientation) could affect whether prey successfully evade predators. We tested this hypothesis by recording the escape responses of juvenile red sea bream (Pagrus major) to the predatory scorpion fish (Sebastiscus marmoratus). Flight initiation distance tended to be small when prey were attacked from behind, suggesting that prey have spatial bias in detecting attacking predators. An increase in flight initiation distance increased escape probability. An increase in initial orientation decreased turn duration and increased escape probability when the effect of flight initiation distance was offset. These results suggest that initial orientation affects escape probability through two different pathways: changes in flight initiation distance and turn duration. These findings highlight the importance of incorporating initial orientation into other studies of the kinematics of predator-prey interactions.

The escape trajectory (ET) of prey - measured as the angle relative to the predator's approach path - plays a major role in avoiding predation. Previous geometric models predict a single ET; however, many species show highly variable ETs with multiple preferred directions. Although such a high ET variability may confer unpredictability to avoid predation, the reasons why animals prefer specific multiple ETs remain unclear. Here, we constructed a novel geometric model that incorporates the time required for prey to turn and the predator's position at the end of its attack. The optimal ET was determined by maximizing the time difference of arrival at the edge of the safety zone between the prey and predator. By fitting the model to the experimental data of fish Pagrus major, we show that the model can clearly explain the observed multiple preferred ETs. By changing the parameters of the same model within a realistic range, we were able to produce various patterns of ETs empirically observed in other species (e.g., insects and frogs): a single preferred ET and multiple preferred ETs at small (20-50°) and large (150-180°) angles from the predator. Our results open new avenues of investigation for understanding how animals choose their ETs from behavioral and neurosensory perspectives.

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Since the escape response is crucial to survival and hence to the fitness of species, several studies have attempted to elucidate the kinematic and behavioral components of the response that affect evasion outcome. The prey’s body orientation relative to a predator at the onset of the escape response (initial orientation) could affect evasion outcome, because the turn angle and its duration before the initiation of escape locomotion would be smaller when the initial orientation is more away from the predator. We tested this hypothesis by recording the escape responses of juvenile red sea bream (Pagrus major) in response to the predatory scorpion fish (Sebastiscus marmoratus) using a high-speed video camera. Our results show that an increased initial orientation (i.e., more away from the predator) increases escape probability. Our results also indicate that an increase in the initial orientation decreases the turn angle and its duration. The flight initiation distance tends to be small when the initial orientation is away from the predator, suggesting that the prey might have a blind zone of sensory perception. These findings highlight the importance of incorporating initial orientation into both empirical and theoretical studies of the kinematics of predator-prey interactions.Summary statementOur predator-prey experiments reveal that the prey’s initial body orientation relative to a predator affects the prey’s turn angle and its duration, and consequently affects escape probability.

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