ORGANOCHLORINE AND HEAVY-METAL CONTAMINATION IN NONVIABLE EGGS AND ITS RELATION TO BREEDING SUCCESS IN A SPANISH POPULATION OF LESSER KESTRELS (FALCO-NAUMANNI)

Residues of organochlorines, polychlorinated biphenyls (PCBs), and hea vy metals (mercury, cadmium, lead, copper and zinc) were measured in u nhatched eggs of Lesser Kestrels (Falco naumanni) collected in souther n Spain in 1988-1991. Although contaminants were detected in all eggs, the amounts were generally below levels known to have negative effect s on reproduction. This is consistent with the relatively high hatchin g rate (about 80%) in the studied population. The nestling mortality w as severe, however, apparently due to starvation. It can-not be discou nted that pesticides had an indirect effect on the kestrel's breeding success by reducing the populations of prey.