Trace Element Concentrations and Bioindicator Responses in Tree Swallows from Northwestern Minnesota |
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Authors: | Christine M Custer Thomas W Custer David Warburton David J Hoffman John W Bickham Cole W Matson |
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Institution: | (1) U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, WI 54603, USA;(2) U.S. Fish and Wildlife Service, 4101 E. 80th St., Bloomington, MN 55425, USA;(3) U.S. Geological Survey, Patuxent Wildlife Research Center, c/o BARC-East, Bldg. 308, 10300 Baltimore Avenue, Beltsville, MD 20708, USA;(4) Department of Wildlife and Fisheries, Texas A&M University, College Station, TX 77843, USA |
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Abstract: | Extremely high concentrations of cadmium (3.5 μg/g dry wgt.) and elevated concentrations of chromium (>10 μg/g dry wgt.) and mercury (1.6 μg/g dry wgt.) were reported in waterbird tissues at Agassiz National Wildlife Refuge in northwestern Minnesota in 1994. Tree
swallows (Tachycineta bicolor) were studied during 1998–2001 at three drainages into the Refuge, two pools on the Refuge, and at a nearby reference location
to document whether high levels of contaminants were still present, and if so to quantify the source and severity of the contamination.
Trace elements were measured in tree swallow eggs, livers, and diet. Reproductive success and bioindicator responses were
monitored. In 2000, water was drawn down on Agassiz Pool, one of the main pools on the Refuge. This presented an opportunity
to evaluate the response of trace element concentrations in the diet and tissues of tree swallows after reflooding. High concentrations
of trace elements were not detected in swallow tissues, nor were there differences among locations. Less than 20% of swallow
samples had detectable concentrations of cadmium or chromium. Mercury concentrations were low and averaged <0.25 μg/g dry wgt. in swallow tissues. Trace elements, including mercury, did not increase in tree swallows following the 2000 drawdown
at Agassiz Pool. Hatching success and survival of nestlings to 12 days-of-age for tree swallows on the Refuge were similar
to the national average and consistent with background trace element concentrations. Bioindicator measurements were within
the normal ranges as well. |
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Keywords: | Agassiz National Wildlife Refuge mercury Minnesota Tachycineta bicolor trace elements tree swallows |
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