Concentrations of polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs) in floodplain soils and sediments are significantly greater downstream of Midland, Michigan (USA) compared to upstream areas. Moreover floodplain soils downstream of Midland have PCDD/DF concentrations 6- to 10-fold greater than those in proximal sediments and are some of the greatest on record. The majority of the contaminant mixture is composed of 2,3,7,8-tetrachlorodibenzofuran and 2,3,4,7,8-pentachlorodibenzofuran, which are likely present in the environment from the historical production, storage, and disposal of industrial organic chemicals and by-products prior to the establishment of modern waste management protocols. The lipophilic nature and slow degradation rates of the PCDD/DFs, combined with the annual inundation of the floodplain, has led to elevated concentrations of PCDD/DFs throughout the basin. In response to concerns regarding the ecological impact of these contaminants a site-specific multiple lines of evidence study was executed including dietary- and tissue-based exposures assessments and population productivity measurement. Two terrestrial [house wrens (Troglodytes aedon) and eastern bluebirds (Sialia sialis)] and one aquatic [tree swallows (Tachycineta bicolor)] food web-based passerine species were monitored both upstream and downstream of the putative source in order to elucidate the potential for contaminant driven adverse population-level effects. Additionally, measured exposures were compared to toxicity reference values (TRVs), and reproductive parameters were compared to literature values. Sixty-nine, 144, and 66 nest boxes were monitored daily at two reference areas (RAs), four Tittabawassee River study areas (SAs), and two Saginaw River SAs, respectively, during the breeding seasons of 2005 through 2007. Concentrations of EPCDD/DF 2,3,7,8-tetrachlorodibenzo- p-dioxin equivalents (TEQ_WHO-Avian) in both eggs and nestlings of the species studied at downstream SAs were 3- to 246-fold greater than RAs, with the exception that tree swallow eggs had similar concentrations among locations. Site-specific average TEQ_WHO-Avian daily dose for house wrens, tree swallows, and eastern bluebirds at downstream Tittabawassee River SAs was at least 45-, 41-, and 70-fold greater than RAs, while Saginaw River SAs were intermediate. Overall reproductive parameters for the three passerine species studied were similar or greater at downstream SAs compared to upstream RAs. Of all initiated clutches 66% (n=427), 73% (n=245), and 64% (n=122) successfully fledged at least one nestling for house wrens, tree swallows, and eastern bluebirds, respectively. Dietary exposure for adult house wrens, tree swallows, and eastern bluebirds were greater than the selected TRVs however the other lines of evidence such as egg-based exposure assessments, productivity, and measures of individual health did not indicate an at risk population. The most probable cause of the apparent dichotomy among the dietary-based exposure assessment and the other lines of evidence was that the dietary-based TRVs selected are likely conservative based on the dose delivery methodology. Ongoing band return rate data will conclude in 2010 and provide additional data on species demographics including information on post-fledging survival and population recruitment.