Data from: Parent birds assess nest predation risk: influence of cavity condition and avian nest predator activity

Skutch (1949) hypothesized that nest predators visually assess parental activities to locate a prey nest, whereas parents modify fitness-related traits to reduce the probability of nest predation. We examined how cavity condition and parental activity interact with avian nest predators to shape the nest success of two coexisting parid species, marsh tits (Poecile palustris) and oriental tits (Parus minor), breeding in nest-boxes during the incubation period. Nest-boxes were manipulated to create a prolonged risk of nest predation (entrance diameter 2.6 cm control vs. 5.5 cm treatment) soon after clutch completion. To measure changes in parental behavior, we also simultaneously simulated a pulsed risk of nest predation, using sound playbacks of a coexisting control bird and an avian nest predator. We found that the parent tits merely responded the pulsed risk, presumably due to an environment with high avian nest predator encounters, compared to the prolonged risk. Instead, both species spent more time on vigilance at the nest, only under prolonged risk conditions. The activity of corvids near the nest-box was higher in the marsh tit than that in oriental tits. This activity was also higher in the treatment nest box than that in the control nest-box. Nest predation during the incubation period was higher in marsh tits than in oriental tits, presumably due to higher and more plastic vigilance in oriental tits, compared to marsh tits. Our results highlight that the differences in cavity condition and parental activities at the nests of two coexisting non-excavators may contribute to differential nest predation by attracting avian nest predators.

斯库奇（Skutch, 1949）提出假说：巢捕食者（nest predator）会通过视觉评估亲鸟活动来定位猎物巢穴，而亲鸟则会调整与适合度相关的性状（fitness-related traits）以降低巢被捕食的概率。本研究针对两种同域分布的山雀科（Paridae）鸟类——沼泽山雀（Poecile palustris）与大山雀（Parus minor），探究了巢箱条件与亲鸟活动如何与鸟类巢捕食者相互作用，进而影响其在孵化期的巢成功率。两种鸟类均营巢于人工巢箱中。本研究于产卵完成后不久，通过操纵巢箱参数设置了长期巢捕食风险：对照组巢箱入口直径为2.6 cm，处理组为5.5 cm。为量化亲鸟行为变化，我们同时采用声音回放法模拟了脉冲式巢捕食风险，分别播放同域共存的对照鸟类与鸟类巢捕食者的鸣叫声。研究结果显示，相较于长期捕食风险，亲山雀仅对脉冲式捕食风险做出响应，这可能与其所处环境中频繁遭遇鸟类巢捕食者有关。与之相反，仅在长期捕食风险条件下，两种山雀均会花费更多时间在巢旁开展警戒行为。巢箱附近鸦科（Corvidae）鸟类的活动频次在沼泽山雀组中显著高于大山雀组；同时，处理组巢箱的鸦科活动频次也高于对照组巢箱。孵化期的巢捕食率在沼泽山雀中高于大山雀，这可能是因为相较于沼泽山雀，大山雀的警戒行为频次更高且可塑性更强。本研究结果表明，两种同域分布的非掘洞筑巢鸟类的巢箱条件与亲鸟活动差异，可能通过吸引鸟类巢捕食者，导致了差异化的巢捕食压力。