Prey jitters; protean behaviour in grouped prey

There have been many descriptive accounts of so-called "protean" or unpredictable escape tactics in prey animals. It is assumed that predators will have difficulty targeting more protean prey either via the prey's escape trajectory and/or via enhancement of the confusion effect (reduced ability to track an individual target in a group of moving and phenotypically similar prey). However, to date no studies have examined whether protean movements decrease predation risk as predicted. In this paper we test, using humans as model predators, whether "protean" prey that have a higher variance in turning angle (and thus change direction abruptly, rather than move on a smoother trajectory) are more difficult to capture and whether this interacts with the confusion effect (previously found using the same model system). We found that protean prey were significantly more difficult to capture. However, protean behaviour did not enhance the confusion effect. We suggest that the primary purpose of protean movements may simply be to make it more difficult for a predator to chase and capture prey, increasing the likelihood predators will give up chase sooner, and that such protean behaviour need not be contingent on prey aggregation. Copyright 2011, Oxford University Press.