Reproductive Success and Eggshell Thinning of a Reestablished Peregrine Falcon Population

Examined numbers of Falco peregrinus pairs, reproductive success, and eggshell thinning in New Jersey during 1979-88. Productivity of these falcons (mean 1.38 young fledged/pair) was comparable with that of stable populations, but productivity was lower for pairs near Delaware Bay and River (0.58 young/pair) compared to those in other regions of New Jersey (1.55 young/pair). Lower productivity and nest success of 4 pairs near Delaware Bay and River studied in both 1987 and 1988 were due to low hatching success and predation, probably by great horned owls Bubo virginianus. During 1985-88 eggshell thickness from New Jersey peregrines averaged 16.4% below pre-DDT levels and apparently has decreased steadily since 1979. This decrease in eggshell thickness statewide suggests that falcons continue to be exposed to environmental contaminants