ABSTRACT
Sixteen-day-old tree swallows (Tachycineta bicolor) were collected in 1999 and 2000 from nine sites within the vicinity of the St. Lawrence River in Canada and the United States to determine if organochlorine contaminant concentrations correlated with corticosterone levels. Basal plasma corticosterone levels were determined in chicks reared in nest boxes, and stress plasma corticosterone levels were determined in chicks after exposure to a 10-min standardized stress test. Mean basal plasma corticosterone concentrations ranged from 4 to 37 ng/ml in 1999, and from 5 to 20 ng/ml in 2000. Mean poststress plasma corticosterone levels ranged from 26 to 67 ng/ml in 1999, and from 26 to 109 ng/ml in 2000. In 1999 and 2000, basal corticosterone was negatively correlated with polychlorinated dibenzofuran (PCDF). Total PCDFs ranged from 4.8 to 120.5 ng/kg wet weight in chicks in 1999 and 2000 among sites. These results indicate that current levels of organochlorine contaminants in the St. Lawrence River and surrounding tributaries may be interfering with the glucocorticoid endocrine axis of tree swallows.