Alaska peregrine falcon productivity in 1984 and the role of organochlorine residues

Twenty Peregrine Falcon (Falco peregrinus) eggs (one per eyrie) were collected at random in Alaska in 1984 for organochlorine residue analysis. Prior to this study we had obtained only addled eggs which were possibly not representative of the egg-laying population if addled eggs contained different levels of organochlorines than viable eggs that hatched. Ten eggs were collected from the American (anatum) population (8 upper Yukon River, 2 Tanana River) and 10 eggs from the Arctic (tundrius) popUlation were later collected in the study area. Productivity at specific eyries and eggshell thickness were evaluated in relation to residue burdens in sample eggs collected. Residue levels and residue profiles for the two subspecies were compared. The tentative 'critical' residue level in Peregrine eggs of 15-20 ppm DDE (wet weight) was compared to results obtained from this study. We also present some data on residue levels in prey species from the study area.