Geographical Variation in Egg Rejection by Azure-winged Magpies (Cyanopica cyanus) across China

Study areaFusong County (42°19ʹ N, 127°15ʹ E) is located in Jilin Province, southeastern China (Figure 1) and is characterized by a continental monsoon climate. The dominant vegetation types are coniferous forests and mixed coniferous-broadleaf forests (Liu et al. 2023). Huangpi District (30°42ʹ N, 114°10ʹ E) is an administrative district of Wuhan, situated in Hubei Province, central China (Figure 1). It is characterized by a subtropical monsoon climate, with dry and cold winters and hot, rainy summers. The dominant tree species include camphor (Cinnamomum camphora), the Chinese parasol tree (Firmiana platanifolia), and the golden rain tree (Koelreuteria paniculata) (Liu et al. 2023a). Luqu County (34°34ʹ N, 102°29ʹ E) is located on the eastern edge of the Qinghai-Tibet Plateau in Gansu Province, southwestern China (Figure 1). It is characterized by a humid plateau climate, with cold and damp conditions. The primary vegetation types include meadows, coniferous forests, and shrublands (Gao et al. 2021).Egg rejection experimentDuring the azure-winged magpie breeding season in April to June, 2023 and 2024, we systematically searched for breeding nests in the study area and recorded the nest coordinates and clutch size. Egg recognition experiments were conducted on nests in the early incubation stage. Previous studies have suggested that the color of model eggs can influence hosts’ rejection decisions (Abolins-Abols et al. 2019; Hanley et al. 2021; Liu et al. 2024; Yan and Liang 2024). To investigate the effects of color on the egg rejection behavior of the azure-winged magpie, we tested the egg recognition abilities in all three study sites using both red and blue model eggs. The experiment was divided into three groups: (1) no model egg was added, and the nest was monitored under natural conditions (Figure 2A); (2) one red model egg was added directly to the nest (Figure 2B); and (3) one blue model egg was added directly to the nest (Figure 2C). We observed the host’s response to the experimental egg over six days. If the model egg remained in the nest on the sixth day without peck marks and the magpie continued normal incubation, it was classified as accepted. If the model egg was missing, showed peck marks, or was buried, it was classified as rejected. Nests that were predated during the experiment were excluded from the analysis (Moksnes et al. 1991).While studies have shown that hosts may adjust their defensive behavior according to parasitism risk, whether different geographical populations of the azure-winged magpie (Cyanopica cyanus), which are parasitized by multiple cuckoo species and face varying parasitism risks, exhibit geographical variation in egg rejection behavior is unclear. From April to June in 2023 and 2024, we investigated the egg recognition ability of azure-winged magpie populations in Fusong County, Jilin Province; Huangpi District, Hubei Province; and Luqu County, Gansu Province, China. The results showed that the azure-winged magpie populations in all three regions rejected approximately 100% of the model eggs, with no significant difference in rejection rates between red and blue model eggs. This study revealed that Chinese populations of azure-winged magpies exhibited high egg recognition ability, with no geographical variation in their egg rejection behavior.