Organochlorine residues and shell thinning in Oregon seabird eggs

Abstract

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.