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Mercury Exposure Affects the Reproductive Success of a Free-living Terrestrial Songbird, the Carolina Wren, (Thryothrus ludovicianus)
Citation:
JACKSON, A. K., D. C. EVERS, M. ETTERSON, A. M. CONDON, S. B. FOLSOM, J. DETWEILER, J. SCHMERFELD, AND D. A. CRISTOL. Mercury Exposure Affects the Reproductive Success of a Free-living Terrestrial Songbird, the Carolina Wren, (Thryothrus ludovicianus). The Auk. American Ornithologists' Union, Shipman, VA, 128(4):759-769, (2011).
Impact/Purpose:
This is the first study to quantify reduced breeding performance associated with individual female blood mercury levels and has wide-reaching conservation implications as global mercury pollution is increasing and songbird populations are declining.
Description:
The impacts of mercury contamination on aquatic-feeding wildlife are well-established, but recent attention has focused on the effects of mercury on species in terrestrial ecosystems. Despite mounting evidence of mercury accumulation in terrestrial ecosystems, there is little data on how environmental mercury exposure affects reproductive success in free-living songbirds. From 2007 2010, we monitored reproductive success of Carolina Wrens (Thryothorus ludovicianus) along two mercury contaminated rivers in Virginia, USA. Using an information theoretic approach, we determined that Carolina Wrens experienced 34% reduction in nest survival on mercury-contaminated sites compared to reference sites lacking mercury contamination from industrial point-sources. Using data collected in 2010 on blood mercury levels of attending female Carolina Wrens, we found that female blood mercury level was a strong predictor of nest survival. Our modeled results indicate that females with approximately 1.3 µg/g mercury in their blood likely experience a 20% reduction in nest survival compared to those with no mercury contamination. Along the approximately linear portion of the response curve (between 0 and 4 µg/g), nest survival decreased by an average of 10% for each 0.5 µg/g increase in blood mercury. Birds nesting on contaminated sites were three times more likely to abandon their nests than birds on reference sites. This is the first study to quantify reduced breeding performance associated with individual female blood mercury levels and has wide-reaching conservation implications as global mercury pollution is increasing and songbird populations are declining.