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

One of the most effective strategies for avian hosts to defend against brood parasitism is to eject the parasitic egg from the focal nest. However, the variation in egg-rejection frequency between individuals remains poorly understood. A precondition for egg ejection is the recognition of 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 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). In addition, redstarts did not change the eye-use preference when inspecting their own eggs or the foreign egg, but they spent longer time inspecting the foreign egg and inspected it more frequently than inspecting their own eggs. Moreover, females with a left-eye preference were more likely to recognize the foreign egg than individuals without an eye-use preference, and individuals who inspected the foreign egg more often were more likely to recognize the egg. Our results demonstrate that the left eye-use preference facilitates the host's ability to recognize the foreign egg.