Print PageMany bird species in North America and worldwide have shown steady population declines, with nearly a third of the 800 bird species in the U.S. classified as endangered, threatened, or in significant decline. Although, habitat loss has been identified as a primary factor, environmental contaminants may also play a role. For example, mercury (Hg) contamination has been suggested as a contributor to population declines, likely due to its negative effect on reproduction. Both natural (volcanic eruptions) and anthropogenic (coal-burning powerplants) processes contribute to atmospheric Hg with the latter likely to increase as Asia continues to increase its emissions.
In this study, we quantified levels of total Hg in blood and feather of resident avian species of multiple trophic levels at three study sites representing temperate (Caddo Lake, Texas; 32°N), Arctic (Thule, Greenland; 77°N), and sub-Antarctic (Puerto Williams, Chile; 54°S) latitudes during 2010 and 2011. We expected Hg levels to increase with increasing trophic levels, and as atmospheric Hg is known to exhibit long-range transport, measurable concentrations of Hg at the polar and sub-polar regions were expected and these levels should correlate to their distance from high Hg emitting regions with areas in Texas having higher levels.
Results/Conclusions
All three areas experienced positive increases in Hg levels with increasing trophic level. At our temperate study site, high trophic level species, including 100% of Great Blue Herons (Ardea herodias; n=7) and 79% of Great Egrets (Ardea alba; n=14), had feather Hg levels above 5000 ppb (mean ± SD: 13140 + 4520 and 7950 ± 4286, respectively). At the Arctic study site, no birds exhibited blood Hg levels above 1200 ppb, even among high trophic feeders, i.e., Thick Billed Murre (Uria lomvia; n=36): 690 ppb + 170. Kelp Gulls (Larus dominicanus; n=21) represent the high trophic level sample collected from Chile. Sample analysis for these birds is in progress.
This study provides evidence that Hg concentrations are elevated at the temperate study site as compared to the Arctic site, particularly in high trophic level species. The currently accepted threshold of 5000 ppb for feather and 3000 ppb for blood Hg concentration are associated with adverse affects including lethargy, suppressed stress response, compromised immune functioning, lower body and organ weights, reproductive failure and male-male pair bonding. The high concentrations observed in this study warrant further investigation due to potential adverse affects on population demographics and recruitment observed in other avian studies.
