Novel effects of monitoring predators on costs of fleeing and not fleeing explain flushing early in economic escape theory

Economic escape theory predicts flight initiation distance (FID, predator–prey distance when fleeing from an approaching predator begins), but currently cannot account for an observed increase in FID as alert distance (AD, predator–prey distance when a prey becomes alert to a predator), or its surrogate, starting distance (SD, predator–prey distance when approach begins) increases. The flush early and avoid the rush hypothesis suggests that FID increases as AD increases due to costs of monitoring the predator. However, the AD–FID relationship and the cost of monitoring have been questioned. Nevertheless, recent evidence shows that FID remains correlated with AD even when spontaneous movements are removed. We discuss possible effects of monitoring that might explain the AD–FID relationship and ways to improve understanding of the influence of spontaneous movements. We disentangle possible effects of 3 distinct phenomena associated with monitoring predators and incorporate them into escape theory. Cost of fleeing might increase as an attentional monitoring cost increases as duration of approach increases. Cost of not fleeing might increase as AD increases due to a physiological cost of monitoring and because assessed risk might increase as duration of approach increases. The attentional cost and effect on assessed risk occur in addition to the effect of decreasing distance in prey that do not account for duration of approach, while assessing costs of fleeing and not fleeing. Some of these effects may operate simultaneously. We describe research needed to better understand the flush early hypothesis and proposed costs associated with monitoring approaching predators.