Are Conspicuous Birds Unprofitable Prey? Field Experiments with Hawks and Stuffed Prey Species

Abstract

The unprofitable-prey hypothesis predicts that birds of prey, when given a choice, should more often attack a cryptic than a conspicuous bird if conspicuousness is a signal of unprofitability. We tested this prediction by exposing pairs of stuffed birds to migrating birds of prey. In experiment 1, we paired the conspicuous White Wagtail (Motacilla alba) with the cryptic Meadow Pipit (Anthus pratensis). In experiment 2, we paired the conspicuous female Great Spotted Woodpecker (Dendrocopos major) with the cryptic female Blackbird (Turdus merula). Automatic cameras documented attacks by birds of prey, mostly accipiters, on the mounts. The numbers of attacks on wagtails and pipits were similar, whereas Blackbirds were attacked much more often than woodpeckers. Experiment 2 thus supports the prediction of the unprofitable-prey hypothesis. Using photographs of the experimental situation, we examined detectability of mounts by human observers. Wagtails and pipits were equally easy to detect from a distance, but woodpeckers usually were easier to detect than Blackbirds. Thus, wagtails and pipits did not differ in "long-distance conspicuousness," which may explain the result of experiment 1. To analyze reasons for unprofitability, we presented flesh from woodpeckers and Blackbirds to captive falcons, but found no evidence that woodpeckers are distasteful. Other explanations for why woodpeckers were rarely attacked are discussed.