Potential cuckoo hosts have similar egg rejection rates to parasitized host species

Background:Thrush species are rarely parasitized by cuckoos,but many have a strong egg recognition ability.To date,there is a limited understanding of the relationship between host egg rejection and cuckoo parasitism rate.Methods:By using egg experiments in the field,we compared egg rejection between two non‑parasitized potential host species and two parasitized hosts of cuckoos in the same region.Results:The White‑bellied Redstart(Luscinia phoenicuroides),a host of the Common Cuckoo(Cuculus canorus),rejected 66.6%of blue model eggs;the Elliot’s Laughingthrush(Trochalopteron elliotii),a host of the Large Hawk Cuckoo(Hierococcyx sparverioides),rejected 25%of blue model eggs and 46.1%of white model eggs;and the Chestnut Thrush(Turdus rubrocanus)and the Chinese Thrush(T.mupinensis),in which cuckoo parasitism has not been recorded,rejected 41.1 and 83.3%of blue model eggs,respectively.There were no significant differences in the egg rejection among them,although the Chinese Thrush showed the highest rate of egg rejection.Conclusions:This study indicates that the egg recognition ability of cuckoo hosts has no correlation with the actual parasitism rate of cuckoos.We suggest that the egg recognition ability of the two potential host species may have been retained from a parasitic history with the cuckoo,while the two common host species have developed their egg rejection abilities due to current parasitism pressure.In addition,our study highlights the importance of the multicuckoo parasite system for better understanding the selection pressure of parasitism on the evolution of host egg recognition abilities.

Nestling discrimination and feeding habits during brooding of Chestnut Thrushes

Background:Nestling discrimination and feeding habits during brooding are important factors affecting host selec-tion of parasitic birds.Some host birds can avoid being parasitized by discriminating their nestlings or feeding food not suitable for parasitic nestlings.Thrushes are common medium-sized birds with widespread distribution and an open nesting habit,but they are rarely parasitized.It remains controversial whether this is due to feeding habits and/or nestling discrimination.Methods:In this study,we tested the nestling discrimination ability and feeding habits of Chestnut Thrushes(Turdus rubrocanus)which is distributed in China’s multi-cuckoo parasitism system.Their nestling discriminability and feeding habits during brooding were studied by cross-fostering experiments and video recording to examine evolutionary restrictions on nestling discrimination and whether feeding habits are consistent with the growth of cuckoo nestlings.Results:Our results indicate that Chestnut Thrushes using earthworms as the main brooding food can feed and maintain cuckoo nestlings and show no nestling discrimination.Conclusions:The present study confirms that feeding habits cannot be regarded as the main factor affecting Chestnut Thrushes being rarely parasitized by cuckoos but suggests that egg rejection is likely to limit the evolution of nestling discrimination in thrushes.