ETHOLOGICAL EVIDENCE FOR SEARCH IMAGES IN PREDATORY BEHAVIOR

Abstract

Publisher Summary Prey abundance changes over time. Many prey species, perhaps in part in response to predator pressures, emerge in sudden population bursts. The expected proportion of such prey in the predator's diet can be calculated as it varies with absolute density, all else being constant. However, it has been found that at low and high prey densities, fewer are caught than expected while at medium densities, the birds are very efficient in catching the particular prey. At low prey densities, the predator underperforms and at increasing densities, the predator begins to catch up and soon over-performs; at high densities, there is a levelling off. In 1971, Murton studied the grain for aging behaviour of wild pigeons in clover and stubble fields. Rigorous testing of the phenomenon of search image formation has been restricted to birds. However, there are a large number of experiments on other animals indicating the possibility that it may be a widespread phenomenon and not just restricted to birds or vertebrates, to visual modality, and to predator–prey relationships. Switching odor preferences has been shown in the large predatory tuna, Thunnus albacares. This fish has exhibited its greatest feeding excitement in response to the odor of the local prey species of anchovy. When fed on a different anchovy species, maximal excitement shifted over the course of about three weeks to the new prey odor. It is possible that pea crabs and tuna form chemical search images; however, the mechanism involved is uncertain.