Egg retrieval as a cognitive indicator in cuckoo hosts

The current study was conducted from March to August during the years 2019–2022 in the Liuzhi area of Guizhou, Southwest China (26°13′ N, 106°42′ E). The sample area is located within the North Temperate Monsoon climate zone at an elevation ranging from 1070.89 to 1657 meters. The region primarily consists of a karst landscape, featuring a mosaic of villages, farmland, scrub forests, and barren slopes (Zhong et al., 2023).This study uses Daurian redstarts (Phoenicurus auroreus), a secondary cavity-nesting host parasitized by common cuckoos (Cuculus canorus), to verify the adaptive decision-making of the host between egg retrieval and egg rejection by simulating the occurrence of eggs outside the nest. Results showed that Daurian redstarts ignored 60.6% of highly mimetic conspecific eggs, with a retrieval rate of only 18.2%. However, non-mimetic budgerigar (Melopsittacus undulatus) and white model eggs were more likely to be directly rejected (75% and 86.4%, respectively) with no retrieval events. Additionally, Daurian redstarts rejected 21.2% of conspecific eggs. Our findings suggest that egg retrieval behavior in Daurian redstarts is significantly influenced by the cognitive process of rejecting parasitic eggs, leading to occasional over-identification and difficulty in distinguishing between egg retrieval and egg rejection, especially in the context of conflicting motivations.