DDE-Induced Eggshell-Thinning in the American Kestrel: A Comparison of the Field Situation and Laboratory Results

Abstract

Because of the stable and lipophilic nature of many organochlorines (Noakes & Benfield 1965; Ecobichon & Saschenbrecker 1968), they show both environmental persistence (Herman, Garrett & Rudd 1968; Dimond & Sherburne 1969) and 'biological magnification' (Hickey, Keith & Coon 1966). By these mechanisms many species of birds of prey have become highly contaminated with organochlorines. Reports of this contamination were paralleled by field observations of eggshell-thinning and consequent reproductive failure (Ratcliffe 1967, 1970; Hickey 1969; Berger et al. 1970; Cade & Fyfe 1970). Cade et al. (1971) reported a strong correlation between eggshell-thinning and egg pp'-DDE content and indicated the need for experimentation on causal relationships. Although DDE-induced eggshell-thinning has been shown experimentally with both predacious (Wiemeyer & Porter 1970; McLane & Hall 1972) and non-predacious birds (Heath, Spann & Kreitzer 1969; Longcore, Samson & Whittendale 1971), the doseresponse relationship has not been characterized nor have captive and wild predators been compared. In choosing a species of predacious bird to study a phylogenetically related species to those showing population decline, such as the peregrine falcon (Falco peregrinus Tunstall) was selected. The American kestrel or sparrow hawk (F. sparverius L.), in addition to being congeneric with the peregrine, is more numerous and readily available and has been successfully bred in captivity (Willoughby & Cade 1964; Porter & Wiemeyer 1969, 1970; Wiemeyer & Porter 1970). The objectives of this study using the American kestrel were to elucidate the doseresponse relationship between dietary DDE and eggshell-thinning, and to compare these laboratory results with egg residues and eggshell-thinning found in a north-eastern population of the same species. In view of the recent controversy concerning the 'real' relationship between DDE and eggshell-thinning (Hazeltine 1972; Wiemeyer & Porter 1972; Switzer, Wolfe & Lewin 1972; Risebrough 1972; Blus et al. 1972), the following data appear timely.