Residue levels of DDE in eggs of Dutch sparrowhawks accipiter nisus following the ban on DDT

Abstract

Dutch sparrowhawk populations were seriously affected by organochlorines during the 1960s. In particular, the role of DDE in suppressing the reproductive output has been often stressed, an effect which was said to prevent sparrowhawk populations from recovering, even after bans on the use of most organochlorines had been enacted.

In the present study residue levels of DDE in eggs were monitored over the period 1975-83, during which time most sparrowhawk populations recovered. Fresh eggs were sampled in three study areas and the contents were analysed for organochlorine compounds.

Since DDE affects egg shells, Ratcliffe indices for shell thickness were measured. Egg breakage frequency was recorded from 1970 to 1983.

From 1975 to 1983 no significant trend in DDE residues, nor in egg-shell thickness, is apparent. The decline in the proportion of clutches with broken eggs suggests a decrease in contamination levels during the early 1970s.

Several causes of the continuing contamination are discussed. DDE is a very persistent compound, and it is likely that considerable amounts are still to be found in the soil and, therefore, in the food chain of the sparrowhawk.