Scale-dependence in polychlorinated biphenyl (PCB) exposure effects on waterbird habitat occupancy

Abstract

Spatial scale is rarely considered in population-level assessments of contaminant impacts on wild animals; as a result misinterpretation of the relationship between contaminant exposure and population status may occur. We assessed the strength of expression of polychlorinated biphenyl (PCB) exposure effects at local vs. regional spatial scales on population status in five species of waterbirds, "bioaccumulators" often promoted as indicators of contaminant effects in aquatic ecosystems. Our focus was the upper Hudson River where PCBs occur at levels reported to have adverse impacts on wild birds. At the local scale, waterbird habitat occupancy was estimated from 220 repeat surveys made between 2001 and 2010 along the same survey route divided into 25 contiguous river segments with markedly different PCB concentrations. At the regional scale, waterbird habitat occupancy in relation to proximity to the upper Hudson River was estimated across 1248 Breeding Bird Atlas survey blocks while controlling for region-wide variation in habitat availability. At the local scale, many associations of habitat and sampling covariates with species detection probabilities were evident but none, including PCB concentration, with habitat occupancy, extinction or colonization of a given river segment. At the regional scale, survey effort and habitat factors not related to PCB exposure were the most important drivers of waterbird occurrence although two species were more likely to occur farther from the contaminated river segment. Spatial scale clearly mediates expression of contaminant impacts on wild bird populations; large-scale, expert-generated databases provide an underused opportunity for better delineating the spatial scales at which population impacts occur and risk assessments should be performed.

Nesting success of red-winged blackbirds (Agelaius phoeniceus) in marshes in an anthropogenic landscape

“…PCBs were released from a nearby Superfund site, designated by the United States Environmental Protection Agency as requiring a long-term action to remediate hazardous contamination [48]. PCB concentrations in the soils and sediments of the investigated portions of the Hudson River and its immediate floodplain are among the highest ever recorded, prompting numerous studies on the effects of PCBs on multiple biota [49,50], including several species of birds [9,51–53]. PCB concentrations in RWBL eggs collected along the upper Hudson River ranged from 0.08 to 34.8 mg kg −1 [54] (see electronic supplementary material, figure S1) and include concentrations with potential for negative effects on nesting success.…”