Eggshell thickness and reproduction in American kestrels exposed to chronic dietary lead.

American kestrels (Falco sparverius) were randomly paired and fed 0, 10, or 50 ppm metallic lead in their diet from November 1979-May 1980. Lead levels were elevated in bones and livers of birds receiving the treated diets, particularly the 50 ppm treatment group. Differential deposition of lead was noted between males and females, with 'l-te highest levels in the females. No adverse effects ere evident with respect to survival, egg laying, or initiation of incubation in any treatment group nor was fertility or eggshell thickness affected. Little or no lead was transferred to the egg contents and although lead was present in the shell, the levels were too variable for this to be considered a useful measure of exposure. Lead is a wide-spread contaminant that enters the environment through a variety of sources. The primary source is from the combustion of lead-containing fuels such as coal, fuel oil, and gasoline (Corrin and Natusch 1977) but less common sources such as lead shot also pose a hazard to wildlife (Bellrose 1959; McConnel 1967). Birds of prey may ingest lead in the form of shot from dead or crippled game animals (Locke et al. 1969; Benson et al. 1974; Jacobson et al. 1977) or biologically-incorporated lead from lead-poisoned waterfowl (29.3 ppm, wet weight, Stendell 1980), roadside small mammals (2.6-34.8 ppm, dry weight, Getz et al. 1977a; Goldsmith and Scanlon 1977). and invertebrates (682 ppm, dry weight, Williamson and Evans 1972). Little is known about the sublethal effects of lead . ngestion on birds of prey but Grand jean ( 1976) reported a correlation between shell thickness and eggshell lead levels in European kestrels (Falco tinnunculus) and suggested that lead may cause shell thinning in raptors. Edens et al. (1976) found lead acetate incorporated in the diet caused a depression in egg production in coturnix quail (Coturnix coturnix) at 1 ppm but inhibition of growth, reduced hatchability, and soft-shelled eggs occurred only at 1.000 ppm. Stone and Soares (1974) also found that 1,000 ppm lead in the diet reduced egg production and caused soft-shelled eggs in coturnix quaiL Morgan et al. (1975) found 500 ppm of dietary lead acetate inhibited growth and produced anemia. In a field study with bam swallows (Hirundo rustica) associated with a heavily-travelled highway, reproductive success was not affected although lead levels were elevated and delta-aminolevulinic acid dehydratase activity depressed 30 to 34 percent (Grue et al., in press). The exposure of birds of prey to lead may be increasing. Peregrine falcons (Falco peregrinus) are being released in eastern United States cities where they prey on starlings (Sturnus vulgaris) and pigeons (Columba Livia), both of which exhibited elevated tissue lead levels in urban environments (Getz et al. 1977b). Bald eagles (Haliaeetus leucocephalus) also are exposed to lead in the dead or crippled waterfowl they consume, sometime receiving lethal levels (Kaiser et al. 1980). Since American kestrels frequent roadsides and many urban areas where elevated lead levels occur, an evaluation of the effects of ingested lead on shell thickness and reproduction was designed. The resulting data should also be useful in assessing the hazards posed by ingested lead to other species of raptors. particularly eagles and peregrines . 1111/IIIIIIIJ~ll !11111111111 j