Site-Specific Assessments of Environmental Risk and Natural Resource Damage Based on Great Horned Owls

Selection of receptors is a key element of ecological risk and natural resource damage assessments. The great horned owl (Bubo virginianus; GHO) has advantages as a tertiary terrestrial receptor and integrated measure of exposure to chemical residues in a multiple-lines-of-evidence approach that includes elucidation of contaminant exposure by measured (tissue-based) and predicted (dietary) methodologies, and population-level measures of potential adverse effects (i.e., productivity, abundance). Methods described herein exploited attributes of GHO behavior, including its propensity to nest in artificial nesting platforms. This approach allowed better control of experimental conditions, minimized uncertainty in assessment endpoints, and maximized data utility for testing hypotheses. During 5 years, 54 GHO nests (14 active territories) along 38 km of river floodplain were monitored at the Kalamazoo River Superfund Site (Kalamazoo/Allegan Counties, Michigan). Concentrations of polychlorinated biphenyls (PCBs) and otho-, para-substituted isomers of dichlorodiphenyltrichloroethane (DDT), including DDD/DDE (Σ DDTs), were measured in 24 eggs and 16 samples of nestling blood plasma. Dietary PCB exposure was predicted by determining site-specific dietary composition and sampling and quantifying PCB concentrations in 171 prey items collected within active GHO territories. The convergence of exposure and effects assessments improved confidence in resulting predictions of minimal risk to resident GHO populations (Hazard Quotients ≤1.5). Repeated GHO use of nesting platforms minimized temporal and spatial variability.