Decline and present status of breeding Peregrine Falcons in Oregon

Unprecedented declines of the Peregrine Falcon (Falco peregrinus) throughout much of the Northern Hemisphere became apparent during the Madison Peregrine Falcon Conference in 1965 (Hickey 1969). Data from Britain were the most detailed; broken or missing eggs were much more common in 1949-56 than they had been in earlier years (Ratcliffe 1958). Subsequently, Ratcliffe (1967) showed a significant decrease in eggshell weight of peregrines in Britain starting in 1947 or 1948. Later, the same finding was demonstrated in North America (Hickey and Anderson 1968). The relation of eggshell thickness to DDE residue levels was established for Alaskan peregrines by Cade et al. (1971) and Peakall et al. (1975). Peakall (1976) stated that pesticides were considered to be a major factor in the decline of the peregrine, and tentatively concluded that the level of DDE in eggs that failed to hatch was 15-20 ppm (wet weight.)