Reproductive ecology of tree swallows (Tachycineta bicolor) with high levels of polychlorinated biphenyl contamination

Tree swallows (Tachycineta bicolor) breeding along the Hudson River forage extensively on PCB-contaminated insects that emerge from the river. We stud ied the reproductive ecology and behavior of tree swallows breeding at seve ral sites along the Hud,on River. Related work has shown that PCB levels in both eggs and chicks were among the highest ever reported in this species, with concentrations comparable to those found in aquatic organisms in the Hudson River. In 1994, reproductive success at PCB-contaminated sites was s ignificantly impaired relative to other sires in New York. Reduced reproduc tive success was largely due to high levels of nest abandonment during incu bation and reduced hatchability of eggs. In 1995, reproductive output was n ormal, but higher than expected rates of abandonment and supernormal clutch es persisted. Growth and development of nestlings was not significantly imp aired. Given the levels of contamination in this population, the success of most Hudson River tree swallows reinforces the importance of understanding interspecific differences in the effects of contaminants.