<b>Risk of cuckoo parasitism does not predict egg rejection behavior in two sympatric breeding 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 <i>et al.</i>, 2023).This study focuses on two sympatric hosts of the common cuckoo (<i>Cuculus canorus</i>), the grey bushchat (<i>Saxicola ferreus</i>) and the black-throated stonechat (<i>Saxicola torquata</i>). 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—2024年3月至8月在中国西南贵州省六枝地区（北纬22°13′，东经106°42′）开展。研究区地处温带季风气候区，海拔范围为1070—1657米，以喀斯特地貌为主，区域内镶嵌分布有村落、农田、灌丛与荒坡（Zhong等，2023）。本研究聚焦大杜鹃（*Cuculus canorus*）的两种同域寄主——灰林䳭（*Saxicola ferreus*）与黑喉石䳭（*Saxicola torquata*）。我们采用拟态程度各异（对应不同卵拒食率）的实验卵，探究这两类寄主是否会依据当前杜鹃寄生风险调整其卵拒食强度。研究结果显示，两种寄主对不同模型卵的拒食率均存在显著差异。但无论使用何种模型卵，杜鹃到来前后寄主的卵拒食率均无显著差异。这一发现表明，杜鹃到来相关的预警线索并未触发寄主卵拒食率的变化。此外，我们还观察到，杜鹃到来后寄主的卵拒食率可能升高，也可能降低。因此，“寄主可根据寄生风险的季节变化调整卵拒食行为”这一假说未得到本研究的支持。未来研究可针对各类寄主的生活史性状展开探究，例如抗寄生适应模式、与年龄结构及婚配制度相关的繁殖经验等，以进一步揭示寄主卵拒食行为季节变化的内在机制。