Evidence for search image in blackbirds ( Turdus merula L.): short-term learning

A ‘search image’ is acquired as a result of a change in the ability of a predator to detect cryptic familiar prey. Blackbirds were presented with artificial prey dyed either to match the colour of the background (cryptic prey) or to contrast with the background (conspicuous prey). The results of experiment 1 provide some evidence that 10 wild blackbirds had more difficulty detecting cryptic prey than conspicuous prey. Detailed analysis of experiments 2 (11 wild blackbirds) and 3 (six captive blackbirds) revealed subtle changes in the reactions of the birds to cryptic prey. At first these birds were unable to detect cryptic prey, but subsequently improved their ability to detect such food. This short-term change is interpreted as evidence for search images.