Changes attributed to pesticides in the nesting success of the sparrowhawk in Britain.
The nesting success of the sparrowhawk (Accipiter nisus) in and near arable areas in Britain has declined since 1947, owing to increased egg-breakage and the failure of incubated eggs to hatch [cf. RAE/A 58, 3735]. In consequence, fewer nests were successful in recent year than formerly and successful broods were smaller. The mean brood size in successful nests was 4.0 up to 1947, 3.2 in 1947-56 and 2.9 in 1956-70. No change was noted in the initial number of eggs in each clutch or in the over-all mortality of the young after hatching. Before 1947, in the absence of human intervention, 100 clutches could be expected to produce 400 young, but in 1956-70 the average was only 160 young, a drop of 60%. No change was apparent in the success of birds nesting in areas remote from arable land, though sample from these areas was small. The change in farmed areas was attributed to contamination of the sparrowhawks nesting there with persistent organochlorine insecticides. While DDT appears to have been associated with shell thinning and egg breakage, deaths of partly formed embryos occurred after the advent of cycloctrenes (aldrin, dieldrin and heptachlor).