A communication-based spatial model of antipredator vigilance.

Many animals spend their lives performing two often mutually exclusive tasks: feeding and watching out for predators (anti-predator vigilance). There have been many theoretical and empirical studies investigating this trade-off, especially for birds. An important characteristic of a flock of real birds is the area occupied by the flock. Individuals feeding close together experience increased competition so that the feeding rate decreases. Widely spaced individuals may suffer a loss in vigilance efficiency, since communication between individuals is more difficult, such that the predation risk increases. A vigilance model is developed which allows birds to control their spacing (and so the area of the flock) as well as their vigilance rate. The best strategy for the birds is found under a variety of environmental conditions, under the assumption that each individual acts selfishly to maximize its own fitness. Copyright 2003 Elsevier Science Ltd.