Prey size selection and competition in the common shrew (Sorex araneus L.)

Summary

• 1. We examine the idea that predators may sometimes use a rule of thumb (in this case prey size) to estimate relative prey profitability for optimizing diet selection. We provided adult common shrews with a choice between large and small pieces of mealworm, where large pieces were less profitable than small, because of handling time characteristics.

• 2. The tendency for animals to prefer large prey depended on their encounter rate with large prey, but was not influenced by variation in encounter rate with small prey once a threshold encounter rate with large (about 0.03 encounters/s) had been reached.

• 3. We also tested the hypothesis that a predator would be less selective when competing with other animals for food. Shrews showed a significant reduction in selectivity when an apparent ‘competitor’ was present during a test.