| Summary: | It is widely accepted that body concentrations of persistent organic pollutants (POPs) tend to increase with trophic level (TL). Yet, little attention has been paid to the causes in the underlying differences in POP body concentrations between species occupying similar TLs. In this paper we use two modeling approaches to quantify the importance of migration and opportunistic feeding, relative to that of trophic level, in explaining interspecific differences in polychlorinated biphenyl (PCB) body concentrations between 6 Arctic seabird species breeding in the Barents Sea: Little Auk ( Alle alle ), Black Guillemot ( Cepphus grylle ), Brünnich’s Guillemot ( Uria lomvia ), Common Eider ( Somateria mollissima ), Black-legged Kittiwake ( Rissa tridactyla ), and Glaucous Gull ( Larus hyperboreus ). As a first approach, we use additive models to analyze two independent data sets ( n = 470 and n = 726). We demonstrate that migration, opportunistic feeding, and TL significantly ( p < 0.001) increase PCB body concentrations by a factor 3.61–4.10, 2.66–20.95, and 2.38–2.41, respectively. Our second approach, using a mechanistic bioaccumulation model, confirmed these positive effects on the body burdens but suggested lower effects of migration, opportunistic feeding, and TL (1.55, 2.39, and 2.38) than did our statistical analysis. These two independent approaches demonstrate that the effects of migration and opportunistic feeding on seabird body burdens can be similar to that of an increase of one TL and should therefore be accounted for in future analyses.
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