REPRODUCTIVE SUCCESS AND EGGSHELL THINNING OF A REESTABLISHED PEREGRINE FALCON POPULATION

Reestablishment of the peregrine falcon (Falco peregrinus) as a breeding bird in the eastern United States is a highlight in endangered species management and recovery programs. We examined numbers of pairs, reproductive success, and eggshell thinning of a reestablished peregrine falcon population in New Jersey during 1979-88. Productivity of these falcons (xBAR = 1.38 young fledged/pair) was comparable with that of stable populations, but productivity of lower (P = 0.02) 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 that we studied intensively 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 decrese in eggshell thickness statewide suggests that falcons continue to be exposed to environmental contaminants.