FRANCESCHINI, M.D.**; CUSTER, C.M.; CUSTER, T.W.; ROMERO, L.M.; Tufts University, Medford, MA; U.S. Geological Survey, La Crosse, WI; U.S. Geological Survey, La Crosse, WI; Tufts University, Medford, MA: Corticosterone Stress Response in Tree Swallows (Tachycineta bicolor) Nesting Near a PCB-Contaminated River

Adult female tree swallows (Tachycineta bicolor) and 11-14 day old nestlings were sampled along the Housatonic River near Pittsfield, Massachusetts at a site highly contaminated with polychlorinated biphenyls (PCBs), from an upstream tributary with mid-range contaminant levels and from a reference site near Great Barrington, MA. A negative relationship between hatching success and PCB levels had previously been documented in tree swallows along the Housatonic River. We collected baseline and 30 min post-capture-stress plasma samples and assayed corticosterone concentrations. Corticosterone did not differ among sites for adult females sampled in 2003. In contrast, nestlings showed a significantly elevated corticosterone stress response at the contaminated site in 2003 (RM ANOVA, P=0.0004, DF=50). In 2004, we measured baseline and 30 min post-injection plasma samples from nestlings injected with (1) saline as a control, (2) dexamethasone and (3) ACTH (adrenocorticotropin hormone). Corticosterone responded similarly to saline and dexamethasone injections at both sites, but stress induced corticosterone levels were reduced at the contaminated site following ACTH injection (RM ANOVA, site P=0.0177, treatment P<0.0001, DF=81). There was an overall difference in years driven by the increased stress response in nestlings at the contaminated site in 2003 (RM ANOVA, P=0.021, DF=74). These findings suggest that tree swallow nestlings chronically exposed to high PCB levels exhibit an altered corticosterone stress response, but the patterns of alteration may be unpredictable.