Dave Warburton, Twin Cities Ecological Services Field Office, and Christine Custer, USGS Upper Midwest Sciences Center, install one of 240 stakes and tree swallow boxes for the trace elements and bioindicators study conducted at Agassiz NWR. - FWS photo by Margaret.Anderson

USGS Scientists Tom and Christine Custer, and FWS Ecological Services Biologist Dave Warburton published this paper (with co-authors D. Hoffman, J. Bickham, and C.Matson) in Enviornmental Monitoring and Assessment (2006) 118:247-266. 

The paper is a result of a study that took place on Agassiz NWR from 1998 to 2001 due to extrememly high concentrations of cadmium and elevated concentrations of chromium and mercury found in waterbird tissues in 1994.   

Two hundred and fourty tree swallow boxes were erected 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. The study also was designed to see if water managment activities, specifically drawdown of pools, resulted in mercury being released into the system.  

Tree swallows are widley used as indicators of local contamination, since they readily use nest boxes which are placed in stratigic locations, and they feed near the site on emergent aquatic instects.  

Eggs and chicks can reflect sediment contamination in a short period of time.  Also, trace element data in this species are available for many locations across the U.S. for comparison. 

RESULTS: High concentrations of trace elements were not detected in swallow tissues, mercury concentrations were low, and there were no increases after a drawdown.