Catching the red eye: field evidence that artificial prey with red eye-like markings are preferentially avoided by avian predators

Calyptrate muscoids (Diptera: Schizophora) are globally distributed flies and among the most maneuverable of flying insects. A salient feature of many calyptrate species is their large red eyes. Given their abundance and evasiveness, it has been postulated that birds might learn to associate the red eye trait with difficulty of capture, and subsequently avoid this prey type. This hypothesis is strengthened by the observation that many arthropods, from spiders to weevils, appear to have evolved a resemblance to calyptrates, including their prominent red eyes. To test the hypothesis directly we pinned 1000 artificial beetles with grey and red eyes onto trees over three separate transects and inspected them 26 days later. As predicted, there was over twice the predation on grey-eyed beetles than red-eyed beetles. The implications of this result are discussed, including how one could quantify the ecological and phylogenetic association between a signaller’s red eyes and its evasiveness.