Data from: Host nest site choice depends on risk of cuckoo parasitism in magpie hosts

Avian brood parasites impose large fitness costs on their hosts and, thus, brood parasitism has selected for an array of host defensive mechanisms to avoid them. So far most studies have focused on antiparasite defenses operating at the egg and chick stages and neglected defenses that may work prior to parasite egg deposition. Here, we experimentally explore the possibility that hosts, as part of a front-line defense, might minimize parasitism costs through informed nest site choice based on perceived risk of cuckoo parasitism. We conducted a large-scale manipulation of visual and auditory cues potentially informing on the risk of great spotted cuckoo Clamator glandarius parasitism during the nest site choice period of the magpie Pica pica host to investigate its effect on host’s nest settlement and individual year to year site fidelity. Early breeding magpies preferentially placed their nests in safe areas (i.e., in sites of low perceived risk of parasitism), and, this effect diluted with time elapsed since risk of parasitism was manipulated. Site fidelity of individual magpies decreased with risk of cuckoo parasitism, for those that were not parasitized in the previous year. Our results constitute the first strong evidence showing that hosts can minimize the costs of cuckoo parasitism through informed nest-site choice, calling for future consideration of defenses potentially operating prior to parasite egg deposition to achieve a better understanding of cuckoo-host coevolution.

鸟类巢寄生者会对其宿主造成巨大的适合度代价，因此巢寄生作用筛选出了一系列宿主防御机制以规避寄生风险。迄今为止，绝大多数相关研究均聚焦于卵期与雏鸟阶段的抗寄生防御策略，却忽视了可能在寄生卵产下前发挥作用的防御机制。本研究通过实验探究了宿主作为第一道防御的一部分，是否可通过基于杜鹃巢寄生感知风险的知情巢址选择来降低寄生成本。我们在宿主喜鹊（Pica pica）的巢址选择期内，对可指示大斑杜鹃（Clamator glandarius）寄生风险的视觉与听觉线索开展了大规模操控实验，以探究其对宿主巢址定居行为以及个体年际巢址忠实性的影响。研究结果显示，繁殖早期的喜鹊优先将巢筑于安全区域（即感知寄生风险较低的位点），且该效应会随寄生风险操控后的时间推移而减弱；对于上一年未遭受寄生的喜鹊个体而言，其年际巢址忠实性会随杜鹃寄生风险的升高而降低。本研究首次提供了确凿证据，证明宿主可通过知情巢址选择降低杜鹃巢寄生的成本，这呼吁未来应重视寄生卵产下前可能发挥作用的防御机制，以更深入地理解杜鹃-宿主协同进化关系。