Avian brood parasitism is a reproductive strategy in which a parasitic species lays its eggs in the nests of a host. In response to parasitism, hosts have evolved various defence strategies. One of the host defences against intraspecific and interspecific brood parasitism is to distinguish parasitic eggs based on intraclutch variation in egg appearance. Hosts can improve their ability to discriminate parasitic eggs by lowering the degree of their intraclutch variation in egg appearance. Therefore, intraclutch variation may affect the egg rejection behaviour of hosts. In this study, we conducted experiments to study egg recognition and rejection behavior for mimetic eggs in Azure-winged Magpies Cyanopica cyanus in Korea. We also investigated the level of variation in egg appearance (egg color, spottiness and volume) in order to explore whether the degree of this variation is associated with the rejection decision. We found that there were no differences in egg coloration or spottiness between the rejecter and accepter. However, we found that intraclutch egg volume variation in rejecters was significantly lower than that in accepters, indicating that the Azure-winged Magpie is likely to recognize its own eggs by lowering its intraclutch variation in egg volume as a defensive strategy against brood parasitism. This study suggests that the Azure-winged Magpie use not the differences in egg coloration but egg volume to discriminate and reject closely mimetic conspecific eggs.
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Vol. 21 • No. 1