Eggshell thinning and organochlorine residues in eggs and prey of Peregrine Falcons from Victoria, Australia

Abstract

The Peregrine Falcon in Victoria is common for a raptor, breeds in most habitats and at a variety of sites and has moderate reproductive success. However, breakage of eggs, loss of clutches and abnormal behaviour of some adults are salient characteristics of the population. Between 1975 and 1977 we collected thirty-five eggs from twenty-six eyries and forty-three individuals of thirteen species of prey for analysis of chlorinated hydrocarbons. Eggshell index averaged 1.52, indicating a 20.4 per cent reduction in shell index from eggs collected before 1952. DDE content of eggs ranged from 2.30-82.00 ppm wet weight (mean 17.63). Polychlorinated Biphenyls and Dieldrin were present in most eggs but at low levels. Residues of DDE for prey were low (mean 0.1 1 ppm) but were highest for two of the most important species in the diet of the Peregrine: Feral Pigeon and Common Starling. Despite rather low use of DDT in Victoria, residues in important prey, specially the Pigeon, are sufficiently high to produce the reproductive failure observed. The significance of this failure to the population of Peregrines is unclear. Its apparent stability probably results from a large population in the past; a future population reduction may occur if eggs continue to be lost at the present rate.