Egg recognition and chick discrimination in colonial breeding birds.

Theory predicts that parents will not raise unrelated offsprings. For colonial breeding birds, evolving an ability to recognize their own eggs and chicks can prevent misdirecting parental behaviour. To verify this hypothesis, egg recognition experiments were performed on colonial breeding Chinese pond herons (Ardeola bacchus) and cattle egrets (Bubulcus ibis) in Chengmai and Lingao, tropical Hainan Island, China. Furthermore, a chick discrimination experiment was conducted on Chinese pond herons. In our study area, we did not record conspecific or interspecific brood parasitism in the two heron species. The results showed that Chinese pond herons had similar recognition rates for the four types of experimental eggs and lacked recognition ability. Cattle egrets had variable abilities to recognize different types of foreign eggs and have low egg recognition ability. Chinese pond herons cannot discriminate foreign chicks. Therefore, we suggest that the two species of colonial breeding herons may lack or have low egg recognition ability, and Chinese pond herons show no nestling recognition ability.