Environmental Monitoring and Assessment

, 118:247

First online:

Trace Element Concentrations and Bioindicator Responses in Tree Swallows from Northwestern Minnesota

  • Christine M. CusterAffiliated withU.S. Geological Survey, Upper Midwest Environmental Sciences Center Email author 
  • , Thomas W. CusterAffiliated withU.S. Geological Survey, Upper Midwest Environmental Sciences Center
  • , David WarburtonAffiliated withU.S. Fish and Wildlife Service
  • , David J. HoffmanAffiliated withU.S. Geological Survey, Patuxent Wildlife Research Center
  • , John W. BickhamAffiliated withDepartment of Wildlife and Fisheries, Texas A&M University
  • , Cole W. MatsonAffiliated withDepartment of Wildlife and Fisheries, Texas A&M University

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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.


Agassiz National Wildlife Refuge mercury Minnesota Tachycineta bicolor trace elements tree swallows