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Mercury Contamination in Tree Swallows Nesting at Northern Wisconsin Inland Lakes that Differ in Methylation Potential
Citation:
CUSTER, T. W., C. M. CUSTER, P. DUMMER, K. P. KENOW, M. W. MEYER, AND R. ROSSMANN. Mercury Contamination in Tree Swallows Nesting at Northern Wisconsin Inland Lakes that Differ in Methylation Potential. Presented at Midwest Chapter of Society of Environmental Toxicology and Chemistry , La Cross, WI, March 30 - April 01, 2009.
Impact/Purpose:
The objectives of this study were to determine mercury concentrations in tree swallow eggs and chicks from nests near lakes with differing methylation potentials and to evaluate the effects of mercury contamination on reproductive success of tree swallows.
Description:
Tree swallows (Tachycineta bicolor) are a useful species to assess the bioavailability and effects of trace elements, including mercury, because they will nest in boxes in relatively close proximity to one another. Because tree swallows feed on the aerial stages of benthic aquatic insects, their tissues reflect what is present and bioavailable in the aquatic system. The objectives of this study were to determine mercury concentrations in tree swallow eggs and chicks from nests near lakes with differing methylation potentials and to evaluate the effects of mercury contamination on reproductive success of tree swallows. In 2007 and 2008, 20 swallow boxes were attached to posts at each of 6 low-pH lakes and 5 neutral-pH lakes in northern Wisconsin. In 2007, 2 eggs per nest were randomly collected from each nest and 2 12-day-old chicks per nest were randomly collected from 5 nests per wetland. Egg contents and tissues from chicks were analyzed for trace elements including total mercury. In 2007, 79% of eggs from low-pH lakes and 88% of eggs from neutral-pH lakes hatched. At low-pH and neutral-pH lakes, 96% of nestlings that hatched survived to 12 days-of-age. Mean mercury concentrations in eggs did not differ between low- (0.28 ppm dry weight) and neutral-pH (0.21 ppm) lakes. Liver concentrations of mercury were significantly higher in chicks from low-pH lakes (0.25 ppm dry weight) than neutral pH lakes (0.13 ppm). Mean nestling blood mercury concentrations were higher at low- (0.028 ppm wet weight) than neutral- (0.008 ppm wet weight) pH lakes.