Organochlorine contaminants and Tree Swallows along the Fox River and Green Bay, Wisconsin, USA

Green Bay, Wisconsin is contaminated with polychlorinated biphenyls (PCBs) however, whether these contaminants affect reproduction in insectivorous birds is unknown. Tree Swallows, Tachycineta bicolor, are secondary cavity nesters that will nest in boxes and tolerate handling. Because Tree Swallows are aquatic insectivores, residues in their tissues are primarily indicative of contaminants in sediments. We studied swallows at two contaminated and two reference colonies in 1993, 1994, and 1995 in the Green Bay area. Swallows at the two contaminated sites had significantly higher PCB levels in eggs when compared to two reference sites. Eggs from clutches that contained dead embryos had higher PCB concentrations than eggs from clutches where all eggs hatched; there were no contaminant effects overall on reproduction, however. Twelve-day-old nestlings at the two contaminated sites accumulated significantly more PCBs than did nestlings at the reference sites demonstrating that PCB contamination came from the local area. The PCB congener profile in 12-day-old nestlings mirrored the congener profile in their food.