Environmental conditions strongly affect antipredator behaviors; however, it is less known how migrating prey adjust antipredator behavior in migration corridors, in part, because active migrants are difficult to observe and study. Migrants are vulnerable and encounter many predators in the corridor, and their propensity to travel towards their destination ties antipredator behavior with movement. We evaluated how environmental risk cues in the migration corridor including in-water habitat structure (present, absent) and overhead shade (sun, shade), and salmon origin (hatchery, wild) affected how juvenile Chinook salmon (Oncorhynchus tshawytscha) reacted to a live predator. We measured how salmon react to predation risk as the difference in time to swim downstream through a 9.1-m long field enclosure with or without a live predatory largemouth bass (Micropterus salmoides). Shade significantly modified the reaction to the predator, and it did so in two ways. First, the magnitude of antipredator behavior was larger in shade compared to direct sun, which suggests salmon perceived shade to be a riskier environment than sun. Second, the escape tactic also varied; salmon slowed down to be cautious in shade and sped up in sun. Structure did not significantly affect behavior and hatchery and wild salmon behaved similarly. Our study suggests that environmental risk cues can shape the magnitude and tactics of how migrants react to predation risk and illustrates how these responses relate to movement with potential to scale up and affect migration patterns.

环境条件强烈影响反捕食者的行为；然而，人们对迁徙猎物如何调整迁徙走廊中的反捕食者行为知之甚少，部分原因是活跃的迁徙者难以观察和研究。移民很脆弱，在走廊里会遇到许多捕食者，他们向目的地旅行的倾向将反捕食者的行为与运动联系起来。我们评估了洄游走廊中的环境风险线索，包括水中栖息地结构（存在、不存在）和头顶阴影（阳光、阴影）以及鲑鱼起源（孵化场、野生）如何影响幼年奇努克鲑鱼（Oncorhynchus tshawytscha) 对活的捕食者有反应。我们测量了鲑鱼对捕食风险的反应，即在有或没有活的掠食性大嘴鲈鱼（Micropterus salmoides）。阴影显着改变了对捕食者的反应，它以两种方式做到这一点。首先，与阳光直射相比，反捕食者在阴影下的行为幅度更大，这表明鲑鱼认为阴影是比阳光更危险的环境。其次，逃跑的手法也多种多样；三文鱼在阴凉处放慢了速度，在阳光下加快了速度。结构对行为没有显着影响，孵化场和野生鲑鱼的行为相似。我们的研究表明，环境风险线索可以塑造移民如何应对捕食风险的幅度和策略，并说明这些反应如何与具有扩大规模和影响移民模式的潜力的运动相关联。