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.
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Data and samples were collected under USGS banding permits 23166 and 26636 and state scientific collecting permit LSSC-10-00034. Thanks to Bill Baggs Cape Florida State Park and particularly Elizabeth Golden for facilitating the migration monitoring and supporting this project. Michelle Davis supervised or personally conducted the migration monitoring and feather sampling in the fall and also supported spring sampling efforts. Erica Hernandez, Robin Diaz, Angel and Mariel Abreu, Felipe Guerrero, and other volunteers assisted in data collection. Mercury analysis was conducted at the Biodiversity Research Institute Wildlife Toxicology Laboratory by Kevin Reagan. Significant improvements to the manuscript were suggested by three anonymous reviewers.
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This study is funded by the University of Maine.
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Adams, E.M., Williams, K.A., Olsen, B.J. et al. Mercury exposure in migrating songbirds: correlations with physical condition. Ecotoxicology 29, 1240–1253 (2020). https://doi.org/10.1007/s10646-020-02190-8
- Bird migration
- Physical condition