Breeding success and organochlorine residue's in golden eagles in West Scotland.
The following is virtually the authors' conclusion and summary. The proportion of eyries of the golden eagle (Aqutta chrysaetos) in western Scotland in which young were successfully reared increased from 31% in 1963-65 to 69% in 1966-68. Concurrently, the level of dieldrin in the eagles' eggs fell from 0.86 part per million (in 1963-65) to 0.34 p.p.m. (in 1966-68). Eagles in eastern Scotland where dieldrin levels in the eggs are extremely low, consistently maintained a high breeding success between 1963 and 1968. No other environmental changes are correlated with the improved success of breeding in western Scotland; in particular, the carrion food supply of eagles before and during incubation shows no parallel. It is therefore concluded that the earlier hypothesis of Lockie & Ratcliffe that contamination by dieldrin ingested with mutton carrion was the cause of a substantial decline in the breeding success of eagles in western Scotland [RAE A 52 584] was correct.