Effects of predator behavior and proximity on risk assessment by Columbian black-tailed deer

Abstract

In predator-prey encounters, many factors influence risk perception by prey and their decision to flee. Previous studies indicate that prey take flight at longer distances when they detect predators at longer distances and when the predator's behavior indicates the increased likelihood of attack. We examined the flight decisions of Columbian black-tailed deer (Odocoileus hemionus columbianus) using an approaching human whose speed, directness of approach, directness of gaze, and simulated gun carrying varied. Deer fled at greater distances when approached more quickly and directly, and there was a concave-down quadratic trend in the relationship between the distances at which the predator began its approach and at which the deer became alert (alert distance [AD]), indicating that deer have a zone of awareness beyond which there is a delay in detecting an approaching predator. Time spent assessing the approacher (assessment time) was shorter during faster approaches and was positively related with AD. Deer fled at longer distances and had shorter assessment times when they were already alert to the predator at the initiation of approach. Males fled at shorter distances than females when approached during the gun-holding condition, and males had shorter assessment times than females when the approacher averted his gaze. Such sex differences in risk assessment might reflect male motivation during the mating season as well as exposure to human hunting. We suggest that risk assessment is affected the by the predator's behavior, the state of awareness of the prey, and the distance at which they detect the predator.