The role of different organo-chlorine compounds in the breeding of British sparrowhawks.
Organochlorine levels and shell thickness indices varied little between eggs in the same clutch of Accipiter nisus in the UK, but they varied greatly among clutches from the same female in different years. Organochlorine levels in eggs tended to increase between first-year and older females. Among 315 clutches the overall ratio of DDE:PCB was 1:0.53, and of DDE:HEOD 1:0.19. The levels of all these compounds were correlated with one another. DDE concentration was related to the extent of shell thinning, egg breakage, egg addling, and hatching failure. PCB concentration was related to the extent of egg addling and hatching failure. There was no relationship between organochlorine levels and the date of the first egg, initial clutch size, frequency of egg desertion and extent of nestling mortality. No relationship could be shown between HEOD concentration and any aspect of breeding examined, but concentrations were low. In only one of nine areas examined was there evidence for a decline in the levels of all three organochlorines during 1971-74, but in the overall sample there was evidence for a decline in PCB levels.