<b>Egg rejection does not change with seasonal variation in risk of parasitism in two sympatric breeding cuckoo hosts</b>

This study was conducted from March to August 2020–2024 in the Liuzhi area of Guizhou, southwestern China (22°13′ N, 106°42′ E). The study area is located in a temperate monsoon climate zone with an elevation range of 1,070–1,657 m. The area is mainly a karst landscape consisting of a mosaic of villages, farmland, scrublands, and barren slopes (Zhong et al., 2023). This study focuses on two sympatric hosts of the common cuckoo (Cuculus canorus), the grey bushchat (Saxicola ferreus) and the black-throated stonechat (Saxicola torquata). Using experimental eggs with varying degrees of mimicry (representing different egg rejection rates), we tested whether these hosts adjusted their egg rejection intensity based on the current cuckoo parasitism risk. Our results showed that both host species exhibited notable differences in rejection rates among various model eggs. However, regardless of the model egg type, no significant differences in egg rejection rates before and after the arrival of the cuckoo was noted. This finding suggests that the presence of cues associated with the arrival of cuckoos does not trigger changes in the hosts’ egg rejection rates. Additionally, we found that egg rejection rates could either increase or decrease after the arrival of the cuckoo. Therefore, the hypothesis of egg rejection adjusting for seasonal changes in parasitism risk was not supported by the present study. Future studies should investigate various host life history traits, such as anti-parasitism adaptation patterns, breeding experiences associated with age structure and mating systems, to further explore the mechanisms underlying seasonal changes in host egg rejection.本研究于2020年3月至2024年8月在中国西南部贵州省六枝地区（北纬22°13′，东经106°42′）开展。研究区域属于温带季风气候区，海拔范围为1070~1657米，以喀斯特地貌为主，镶嵌分布有村落、农田、灌丛与荒坡（Zhong等，2023）。 本研究聚焦于大杜鹃（Cuculus canorus）的两种同域宿主——灰林䳭（Saxicola ferreus）与黑喉石䳭（Saxicola torquata）。研究人员使用拟态程度各异的实验卵（用以代表不同的卵拒斥率水平），探究这两种宿主是否会根据当前的杜鹃寄生风险调整其卵拒斥强度。研究结果显示，两种宿主对不同模型卵的拒斥率均存在显著差异。不过，无论模型卵类型如何，杜鹃到达前后的卵拒斥率均无显著差异。这一发现表明，与杜鹃到来相关的线索并未引发宿主卵拒斥行为的改变。此外，研究还发现，杜鹃到来后，宿主的卵拒斥率可能升高或降低。因此，本研究不支持“宿主卵拒斥行为随寄生风险季节变化而调整”这一假说。未来研究应探索各类宿主生活史性状，例如抗寄生适应模式、与年龄结构和婚配制度相关的繁殖经验等，以进一步揭示宿主卵拒斥行为季节变化的内在机制。