Many migratory songbirds are at high risk of methylmercury (MeHg) exposure due to their trophic position and foraging in and around wetland habitats. Methylmercury has the potential to alter migratory behaviors and physiology via neurological impairment or reduced flight performance and can be remobilized from songbird muscle tissue during migration, increasing the risk of acute MeHg exposure. To document MeHg exposure and its relationship with physical condition in migratory songbirds, we sampled passerine blood and feathers at a migration stopover site on Key Biscayne, FL during fall and spring from 2009 to 2012. We found evidence that spring blood total mercury (THg) concentrations decreased throughout the day and that fall feather THg concentrations changed over the migratory season. Total mercury exposure was marginally correlated with migratory fat stores and related to changes in pectoral muscle thickness by time of day. These patterns suggest that environmentally relevant levels of THg are related to, and may be influencing, the physical condition of free-living migrating songbirds. Further research and monitoring during the migratory period will be important to elucidate exposure risk across multiple species and assess the potential for effects during this complex period of the annual cycle.

许多迁徙鸣鸟由于营养位置和在湿地栖息地及其周围觅食而面临着甲基汞（MeHg）暴露的高风险。甲基汞有可能通过神经功能障碍或飞行性能降低而改变迁徙行为和生理机能，并且在迁移过程中会从鸣禽的肌肉组织中迁移出来，增加了急性暴露于甲基汞的风险。为了记录MeHg暴露及其与迁徙鸣禽的身体状况之间的关系，我们在2009年至2012年秋季和春季的佛罗里达州比斯坎湾的迁徙中转站采样了雀形目血液和羽毛。我们发现了春季血液中总汞（THg）的证据浓度全天下降，并且秋天的羽毛THg浓度在迁徙季节变化。总汞暴露量与迁徙脂肪储存量略有相关，并与一天中的胸肌厚度变化有关。这些模式表明，与环境相关的THg水平与自由生活的鸣禽的身体状况有关，并可能影响这些状况。对于迁徙期的进一步研究和监测，对于阐明跨多个物种的接触风险并评估在这一复杂的年度周期期间的影响潜力至关重要。