Potential Effects of Mercury on Threatened California Black Rails |
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Authors: | Danika C Tsao A Keith Miles John Y Takekawa Isa Woo |
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Institution: | (1) Davis Field Station, Western Ecological Research Center, US Geological Survey, University of California, One Shields Avenue, Davis, CA 95616, USA;(2) San Francisco Bay Estuary Field Station, Western Ecological Research Center, US Geological Survey, 505 Azuar Drive, Vallejo, CA 94592, USA |
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Abstract: | San Francisco Bay (SFB) estuary sediments contain high levels of mercury (Hg), and tidal marsh resident species may be vulnerable
to Hg contamination. We examined Hg concentrations in California black rails, a threatened waterbird species that inhabits
SFB tidal salt marshes. We captured 127 black rails during the prebreeding and postbreeding seasons and examined the influence
of site, sex, and year on Hg, methylmercury (MeHg), and also selenium (Se) concentrations in feathers and blood. Feather Hg
concentrations averaged 6.94 μg/g dry weight (dw) and MeHg and Se concentrations in blood averaged 0.38 and 0.42 μg/g wet
weight (ww). We used Akaike’s information criterion model selection process to evaluate the importance of year, site, sex,
and age on patterns of MeHg concentrations; sex and year were the most important of these factors. Feather Hg concentrations
(dw) were higher in males (8.22 μg/g) than females (6.63 μg/g) and higher in adult birds (7.36 μg/g) than in hatch-year birds
(4.61 μg/g). A substantial portion of SFB black rail populations may be at risk of reproductive effects due to MeHg contamination,
as 32–78% of feathers and <10% of blood samples exceeded no observed adverse effect levels. Sea level rise and other anthropogenic
threats to endemic tidal marsh species such as black rails may be exacerbated by the presence of MeHg. Further study of population
demographics and toxicological effects would further elucidate the effects of MeHg contamination on black rail populations
in SFB. |
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