Optimal Prey Choice and Discrimination Time in the Great Tit (Parus major L.).

1. We tested the predictions of an optimal diet model which incorporated time taken to discriminate between prey types. Five captive great tits were presented with a choice of two prey types. The prey were large (profitable) and small (unprofitable) pieces of mealworm inside pieces of plastic drinking straw. 2. When the worms were inside clear plastic straws, the birds selected only large worms, as predicted by the optimal diet model. When the straws were opaque, so that the birds had to spend time discriminating between large and small worms, four out of five individuals became, as predicted, unselective. The fifth individual had a short enough discrimination time for selection to be the optima policy. 3. An attempt to alter the encounter rate with profitable opaque straws so that birds would resort to selective foraging was not successful because discrimination time for most individuals was too long for the model to predict selection. [ABSTRACT FROM AUTHOR]