Eye-use preference and egg-inspection frequency predict egg recognition in a cuckoo host

Abstract One of the most effective strategies for avian hosts to defend against brood parasitism is to reject the parasitic egg from the focal nest. However, much of the variation in egg-rejection frequency between individuals remains unexplained. A precondition for egg ejection is recognizing the parasitic egg. Previous studies have shown that the left and right eye function differently when recognizing different objects, but few studies have tested the relationship between eye-use preference and egg-rejection probability. In this study, we investigated the relationship between eye-use preference and egg-rejection propensity in the Daurian redstarts Phoenicurus auroreus, a common host of the common cuckoo Cuculus canorus. We found that redstarts exhibited an eye-use preference when inspecting eggs, but without a clear direction of the preference (left/right). After adding a foreign cuckoo egg model, redstarts did not vary either the direction or the strength of the eye-use preference when inspecting the egg, but a spent longer time inspecting and inspected it more often. Moreover, females with a left-eye preference, more frequently and spent more time inspected it when inspecting the parasitic egg were more likely to recognize the foreign egg. Our results thus demonstrate that the left eye-use preference and inspect eggs facilitates the host's ability to recognize the foreign egg.