Evaluating temporal and spatial margins of safety in galahs

When approached by a potential predator, individuals must decide when to flee. Individuals could assess risk by monitoring their distance from an approaching threat or by monitoring the expected time that the predator would take to reach them. Theory predicts, and empirical studies support the hypothesis, that some species may maintain a temporal margin of safety and therefore monitor the expected time a predator would take to reach them. We systematically walked towards galahs, Cacatua roseicapilla, an Australian parrot, and varied our approach speed. If galahs maintain a temporal margin of safety, we expected them to flush at a greater distance in response to the fast approach. We found, however, no support for the temporal margin of safety hypothesis. Rather, we found evidence that galahs are sensitive to distance in a novel way: after being alerted, they flushed when humans approached to within 44% of the alert distance. Our result differs from traditional models of spatial margins of safety because it suggests that animals will take flight after being approached to within about half the alert distance. By doing so, individuals maintain a dynamic spatial margin of safety and may reduce costs associated with ongoing monitoring of predation risk. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.