PREY AVAILABILITY AND SELECTIVE FORAGING IN SHOREBIRDS

Accurate measurements of prey availability are vital to our understand ing of foraging behaviour, particularly prey selectivity. In the prese nt study, observations of shorebirds foraging for fiddler crabs on int ertidal mudflats demonstrate that prey availability depends both on th e temporal variation in crab activity and on the crabs' responses to t he presence of foraging shorebirds. Our results suggest that measureme nts of prey availability that do not specifically account for prey act ivity patterns and their responses to predators are neccessarily inacc urate. Furthermore, our results also show that tests for foraging sele ctivity are extremely sensitive to the way in which prey availability is measured and can even indicate active prey selectivity when more ac curate measures of prey availability show predators to be non-selectiv e. Because inaccurate measures of food resources greatly reduce our ab ility to detect food preferences, greater care must be taken to accoun t for prey activity patterns and their responses to predators in measu rements of prey availability. (C) 1998 The Association for the Study o f Animal Behaviour.