Abstract
Saltmarsh sparrows (Ammospiza caudacuta) and seaside sparrows (A. maritima) are species of conservation concern primarily due to global sea-level rise and habitat degradation. Environmental mercury (Hg) contamination may present additional threats to their reproductive success and survival. To assess site-specific total mercury (THg) exposure and identify environmental correlates of THg detection, we sampled blood from adult male saltmarsh and seaside sparrows at 27 sites between Maine and Virginia, USA. The mean THg concentration (±1 SD) throughout the entire sampling range was 0.531 ± 0.287 µg/g wet weight (ww) for saltmarsh sparrows and 0.442 ± 0.316 µg/g ww for seaside sparrows. Individual THg concentrations ranged from 0.135-1.420 µg/g ww for saltmarsh sparrows and 0.153-1.530 µg/g ww for seaside sparrows. Model averaging from a suite of linear mixed models showed that saltmarsh sparrows averaged 20.1% higher blood THg concentrations than seaside sparrows, potentially due to differences in diet or foraging behavior. We found no evidence for a relationship between sparrow THg concentrations and land cover surrounding sampled marshes or average precipitation-based Hg deposition. Overall, our results suggest considerable, unexplained variation in tidal marsh sparrow blood THg concentrations over their co-occurring breeding ranges.
Highlights
Mercury (Hg) is a widespread environmental contaminant that can pose a threat to wildlife by affecting neurological and reproductive systems (Evers 2018)
Individual total Hg (THg) concentrations ranged from 0.135–1.420 μg/g ww for saltmarsh sparrows and 0.153–1.530 μg/g ww for seaside sparrows
Our conditional model-averaged results indicated that saltmarsh sparrows tended to have higher blood THg concentrations than seaside sparrows both when present at the same marsh sites and across their ranges (Table 1, Appendix 2)
Summary
Mercury (Hg) is a widespread environmental contaminant that can pose a threat to wildlife by affecting neurological and reproductive systems (Evers 2018). Sulfate-reducing bacteria accelerate the production of MeHg (Compeau and Bartha 1985), leading to elevated risks for organisms living in, around, or feeding from contaminated wetlands. Both the saltmarsh sparrow (Ammospiza caudacuta) and seaside sparrow (A. maritima) are tidal marsh specialists and spend their entire life cycles within saltmarsh habitats, where risk of exposure to MeHg can be elevated. Anthropogenic activities including coastal development, marsh fragmentation, and alteration of hydrology have all reduced habitat available for both saltmarsh and seaside sparrows
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