DIRECTION OF PREDATOR APPROACH AND THE DECISION TO FLEE TO A REFUGE

How close should an animal allow a potential predator to approach befo re fleeing to a refuge? Fleeing too soon wastes time and energy that c ould be spent on other important activities, but fleeing too late is p otentially lethal. A model to predict flight initiation distance was d eveloped, based on the assumption that animals would flee at a distanc e that allows them to reach the refuge ahead of the predator by some m argin of safety. This model predicts that (1) flight initiation distan ce should increase with distance from the refuge (which has been suppo rted by studies on several species) and (2) the rate of increase of fl ight initiation distance with distance from a refuge should be higher when the refuge is between the predator and prey (prey runs towards th e predator) than when the prey is between the predator and the refuge (prey runs away from the predator). Prediction 2 was tested by approac hing juvenile woodchucks, Marmota monax, along an imaginary line betwe en the animal and its burrow entrance and measuring the distance betwe en the observer and the animal at the moment it started its flight. As predicted, the rate of increase in flight initiation distance was hig her when the burrow was between the observer and the woodchuck than wh en the woodchuck was between the observer and the burrow. The slopes w ere appropriate for predators with pursuit speeds about twice the esca pe speed of the woodchucks. The difference between the slopes was 1.78 m flight distance/m distance to refuge, close to the value of 2 m fli ght distance/m distance to refuge predicted by the model. The intercep t indicated that woodchucks allowed a margin of safety of about 7.6 m. The model permits quantitative evaluation of the principal elements o f flexible escape decisions of animals and provides a measure of how p redation risk increases the cost of space use in relation to distance from a refuge. (C) 1997 The Association for the Study of Animal Behavi our.