Organochlorines and mercury in the eggs of British Peregrines Falco peregrinus

Abstract

The levels of various contaminants were measured in 550 addled and deserted PeregrineFalco peregrinuseggs obtained in Britain during 1963‐86. In this period the population was recovering from a low level imposed by organochlorine pesticides. Over the whole period, HEOD levels declined in eggs from both inland and coastal regions, while DDE levels declined in eggs from inland regions. At the same time, shell‐indices improved. PCB levels increased in eggs from inland regions. At any one time, levels of DDE and HEOD in eggs decreased and shell‐indices increased from south to north within Britain. These gradients fitted with the extent of agricultural land (= pesticide use) and with the extent of Peregrine population decline (both greatest in the south). No south‐north trend was apparent in levels of PCBs derived from industrial sources. In some regions eggs from coastal sites were more contaminated than eggs from inland sites, especially with PCBs and mercury. Significant relationships were found between brood sizes and DDE levels, between brood sizes and shell‐indices, and between shell‐indices and DDE levels. This implied that DDE influenced shell thickness and breeding success. Some evidence was obtained that mercury reduced brood sizes, but no evidence that HEOD and PCB (at the levels found) did so. Overall, DDE and mercury levels together accounted for 17% of the variance in brood sizes during 1963‐86. On a regional basis, DDE had no obvious effect on mean productivity when the geometric mean DDE level in collected eggs was less than 3 p.p.m., and when mean shell‐index was no more than 8% less than normal. At higher DDE levels, and lower shell‐indices, productivity declined markedly. Recovery of regional populations was associated with geometric mean HEOD levels in eggs no greater than 0–7 p.p.m., DDE levels no greater than 15 p.p.m., shell indices no more than about 15–20% below normal, and a mean breeding success exceeding 0–6 young per territorial pair.