Mercury exposure in migrating songbirds: correlations with physical condition
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Mercury exposure in migrating songbirds: correlations with physical condition Evan M. Adams1,2 Kathryn A. Williams2 Brian J. Olsen1 David C. Evers2 ●
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Accepted: 28 February 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract 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 freeliving 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. Keywords Mercury Bird migration Songbirds Stopover Physical condition ●
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Introduction Migration, including both active flight and stopover periods, is an energetically costly and physiologically demanding life history period for songbirds that is characterized by high mortality (Wikelski et al. 2003, Jenni and Schaub 2003, Sillett and Holmes 2002). Migrants undergo a range of physiological and behavioral changes to sustain migration. These adaptations include adjustments to metabolism, nutrition, and morphology; many of these changes relate to the storage, mobilization, transport, and usage of energy (Weber 2008). Roughly 90% of the energy used during
Supplementary information The online version of this article (https:// doi.org/10.1007/s10646-020-02190-8) contains supplementary material, which is available to authorized users. * Evan M. Adams [email protected] 1
School of Biology and Ecology, Climate Change Institute, University of Maine, Chadbourne Hall, Orono, ME, USA
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Biodiversity Research Institute, 276 Canco Rd., Portland, ME 04103, USA
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migratory flight is drawn from fat stores, rather than protein, but muscle mass changes can be significant as well (Guglielmo 2018). Exposure to toxic global pollutants like mercury (Hg) has the potential to disrupt complex migratory behaviors and processes in several ways. Long-distance migratory birds appear to be uniquely vulnerable to Hg, possibly due to diet (Knutson 201
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