Organochlorine residues in Alaskan peregrines.

Organochlorine residue levels in eggs of Alaskan peregrines have remained essentially constant over the period 1969-73 despite decreased usage of these compounds in the United States and Canada. Studies on reproductive success in Great Britain and data on eggshell-thinning suggest that DDE residues above 20 ppm wet weight in peregrine eggs are associated with inability to maintain population levels. Residues in mainland Alaska are well above this critical figure and the reproductive rate is low. On the Colville River in northwestern Alaska, the last young falcons will fledge in 1975 and the remaining adult population will disappear by 1980 unless the present rate of reproductive failure is drastically and quickly reversed. In the Aleutians, however, levels range from 5 to 7 ppm and the reproductive rate is adequate to maintain the population.