Visual monitoring of predators: occurrence, cost and benefit for escape

Escape theory assumes that prey monitor predators to assess risk, but surprisingly little is known about cost and benefits of monitoring behaviour. I simulated a predator to examine effects of impaired monitoring on escape and use of monitoring behaviour by the lizards Sceloporus virgatus and S. jarrovii. For approaches (from directly behind or ahead) impeding or preventing monitoring, flight initiation distance in S. virgatus was shorter than that for approaches from the side, establishing a benefit of monitoring. Distance fled by S. virgatus was longer for approaches from the side than for those from ahead or behind. This effect was not predicted by escape theory or the margin of safety hypothesis, but it does not contradict either because neither applies when monitoring is impossible. Lizards may have fled a short distance upon detecting predators previously out of view and then stopped to monitor and assess risk. Both species cock their heads (turn them to the side) to bring objects into view, providing a visible marker for monitoring. They head-cocked to reestablish monitoring within seconds of losing visual contact. After fleeing behind rocks, they exposed only their heads upon emerging, which enabled monitoring with reduced likelihood of being detected and reduced exposure if attacked. Thus, prey monitor predators even when doing so increases risk of being detected, implying trade-offs between risk caused by monitoring and benefits of information. The findings emphasize the value of current information on predator location and complement information about risk assessment based on alert distance.