Organochlorine residues and shell thinning in Oregon seabird eggs

A single egg was collected at 62 nests of 10 seabird species from Oregon in 1979. The eggs were analyzed for organochlorine contaminants; contemporary shell thickness was compared with eggshells collected during earlier time periods. Concentrations of DDE and PCB's in 1979 were generally low with the most contaminated species being the Double-crested Cormorant (Phalacrocorax auritus), Leach's Storm Petrel (Oceanodroma leucorhoa), and Forktailed Storm Petrel (O. furcata). Limited eggshell data provide evidence that shell thinning was more severe along the Oregon coast in the 1950's than in 1979. With the possible exception of the Fork-tailed Storm Petrel, the residues in 1979 posed no known threat to the welfare of the species.