Polychlorinated biphenyl exposure and effects in tree swallows (Tachycineta bicolor) residing at eight locations

Twelve-day-old Tree Swallow nestlings were studied at eight sites exhibiting a range of polychlorinated biphenyl (PCB) contamination. In addition to determining PCB concentrations in eggs, nestlings, and food items, hepatic cytochromes P450-associated monooxygenase activity quantified as a biomarker of exposure. Nestlings from several of the sites exhibited elevated PCB concentrations and P450 induction compared to a reference site, Furthermore, cytochromes P450 were correlated with PCB concentrations in nestling. Our findings indicate that likely routes of exposure include the direct materna! deposition of PCBs into the egg and the delivery of contaminated emerging aquatic insects to nestlings. We also examined reproductive and morphological parameters to determine if PCB exposure was adversely affecting swallows at these sites. Hatching success did not differ among sites. There were no dramatic effects on gross and histological gonadal morphology of nestlings, and there was complete concordance between phenotypic sex (gonadal morphology) and genotypic sex (as determined by PCR amplification of the sex chromosome). However, where nestling PCB exposure was substantial, clutch size and body weight differed from a reference site. Despite evidence of PCB exposure, only modest effects were observed in nestling swallows.