Breeding success and organo-chlorine residues in golden eagles in west Scotland.
The same 25 eyries of golden eagles (Aquila chry-saetos) were examined each year in west Scotland. In 1963-65 the "percentage of nests with eggs from which young flew" was 31 and that of nests with eggs was 39%; in the eggs analysed the mean concentration of dieldrin was 0.86 ppm. In 1966-68 the corresponding values were 69%, 45 and 0.34 ppm. For each year, from 1963-68 inclusive, are given the percentage of nests with eggs from which young flew, number of nests with eggs, number of deer or sheep carcasses per 10-mile transect, percentage of known fox dens occupied and number of dens examined. The dens were all in Wester Ross where 67% of the eyries were.
Breeding success was not related linearly to amount of carrion or breeding density of foxes. It was concluded that dieldrin in carrion had been the cause of the decline in the breeding of eagles. An appendix gives for 49 different places or dates in east Scotland in 1963-65 and for 33 in west Scotland in 1966-68 the content of pp'-DDE, pp'-DDT, dieldrin, heptachlor epoxide, isomers of benzene hexachloride, PCB and total residues in ppm fresh weight of golden eagle's eggs.-M. S.