Bioenergetics-Based Model for Accumulation of Polychlorinated Biphenyls by Nestling Tree Swallows, Tachycineta bicolor

A bioenergetics-based model was developed to simulate the accumulation of polychlorinated biphenyls by nestling tree swallows (Tachycineta bicolor). The model was largely parameterized using published information for passerine birds and accurately describes the observed growth of nestling swallows. The model was evaluated by comparing predicted concentrations of selected congeners with those measured in 15 d-old nestlings collected from two sites within the Saginaw River watershed. Residue concentrations in nestlings were calculated as the sum of compound inherited in the egg and that assimilated from the diet, consisting principally of emergent aquatic insects. Model predictions were in good agreement with those measured in nestlings collected from a relatively uncontaminated site but consistently overestimated concentrations in birds from an area of known sediment contamination. The cause of this discrepancy is unknown, but did not appear to be related to metabolic biotransformation of individual congeners. Instead, it is suggested that dietary composition may have varied between sites. Alternatively, food consumption by nestling birds may have been overestimated. The results of this study indicate that caution must be used when interpreting residue information from nestling swallows, which have been proposed for use as sentinels of local sediment contamination.