Optimal prey selection: Why do great tits show partial preferences?

It is suggested that the partial preferences shown in this specific experiment are due to the combined action of satiation and prey misidentification: as the birds satiate they appear to aim less and less at a maximal energy intake rate; they apply an increasingly stringent criterion which leads to a shift of diet.

Abstract

Contrary to the predictions of optimal foraging theory, great tits (Parus major) in an experimental feeding situation show partial preferences: instead of treating all items of a given prey type in the same way, they take some and reject others. We examine experimentally whether misidentification of prey items or sampling of presentation schedules alone can account for this result. They cannot, and we therefore conclude that a factor other than energetic efficiency is influencing the foraging behaviour. This idea is supported by the finding that hungry great tits follow the predictions of energetic efficiency more closely than partially satiated ones. We suggest that the partial preferences shown in this specific experiment are due to the combined action of satiation and prey misidentification: as the birds satiate they appear to aim less and less at a maximal energy intake rate; they apply an increasingly stringent criterion which leads to a shift of diet.