Reproductive success and chlorinated hydrocarbon contamination in tree swallows (Tachycineta bicolor) nesting along rivers receiving pulp and paper mill effluent discharges

The insectivorous tree swallow was chosen as an indicator species to invest igate the uptake of pulp mill-related chlorinated hydrocarbons from emergen t aquatic insects. Nest box populations were monitored for reproductive suc cess at locations upstream and downstream of pulp mills on two river system s in British Columbia, Canada. Also, 16-day-old nestlings were collected an d analysed for polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p- dioxins (PCDDs) and dibenzofurans (PCDFs), pesticides, chlorophenols and ch loroguaiacols. Most reproductive parameters were not different between popu lations at upstream and downstream locations, and were equivalent to or gre ater than those recorded for other tree swallow populations. Chlorinated hy drocarbon contamination of nestlings was low at all sites. The highest tiss ue concentrations were detected downstream of pulp mills on the Fraser Rive r, where PCDD and PCDF patterns along with the presence of pentachloropheno l (PCP) suggested that the primary source of contaminants was past use of P CP for timber preservation. Although the absolute tissue concentration of c ontaminants was less, the toxic concentration (as estimated with I-TEQs) wa s greatest in nestlings downstream of a pulp mill on the Thompson River. Th e proportionately larger contributions from 2,3,7,8-TCDF and PCB-77 elevate d these TEQs in comparison to other populations. Nest success was the one r eproductive measure that showed substantial reductions in downstream popula tions on both rivers; however, there was little indication that nest failur es were the direct result of contamination. Failures were largely due to pa rental abandonment, and, while poor parental attentiveness and nest abandon ment have been associated with chlorinated hydrocarbon tissue concentration s in other studies, our 1-year assessment was insufficient to establish any link with pulp mill effluent exposure. Nestling growth models showed some subtle differences in growth patterns between nest box populations on the t wo rivers, but an association with pulp mill effects on aquatic insect prey availability was not established. (C) 2000 Elsevier Science Ltd. All right s reserved.