Mortality from the pesticides aldrin and dieldrin in British Sparrowhawks and Kestrels.

Among 1029 dead Sparrowhawks and 1055 dead Kestrels from various parts of Britain that were examined over the period 1963-90, the main causes of death were (a) collisions of various kinds (b) starvation or disease and (c) organochlorine poisoning. The main chemical which caused poisoning was HEOD, derived from the insecticides aldrin and dieldrin. Other deaths were attributed to poisoning by DDE (the main metabolite of the insecticide DDT) and by HE (heptachlor epoxide, derived from the insecticide heptachlor). Sparrowhawks whose deaths were attributed to HEOD poisoning contained 5-85 µg g(-1) HEOD in their livers (wet weight), while Kestrels contained 6-99 µg g(-1) HEOD. Such birds were typically lighter in weight than collision victims, but heavier than starved or diseased birds. In the period 1963-75, HEOD probably accounted for about 50% of all recorded Sparrowhawk deaths and 39% of all recorded Kestrel deaths in eastern arable districts, but a smaller proportion elsewhere. Geographical variation in the proportion of deaths attributed to HEOD paralleled variation in the proportion of land devoted to arable crops on which aldrin and dieldrin were mainly used. It also paralleled variation in the extent of population decline in these species. Moreover, the proportion of deaths attributed to HEOD declined between 1963-75 and 1976-86, following a marked reduction in aldrin-dieldrin use, and fell to nil in 1987-90, when aldrin and dieldrin were withdrawn altogether. Over this period, the populations of both species recovered from a decline which occurred in the late 1950s, when aldrin-dieldrin were first introduced.