Relationships between productivity, eggshell thickness and pollutant contents of addled eggs in the population of white-tailed eagles Haliaëtus albicilla L. in Finland during 1969–1978

Abstract

Eggshells of Finnish white-tailed eagles Haliaëtus albicilla from the 1970s were 16–19·7% thinner than those laid before 1935. During the ten-year study period (1969–1978) eggshell thickness increased in four territories and was stable or decreased slightly in two. Productivity and nesting success increased in these six territories and that of the whole population (about 15 pairs) increased slightly. Arithmetic and geometric mean pollutant concentrations (ppm) of addled eggs were as follows: total mercury 0·80/0·68 (ww) and 2·59/2·35 (dw), PCB 49·1/49·7 (ww) and 583/534 (fw), DDE 38·1/30·0 (ww) and 452/251 (fw), respectively. The DDE content of eggs decreased during the 1970s but PCB and t-Hg contents were stable. It is suggested that the decreasing DDE content is the most obvious reason for the increasing productivity because of the improved viability and hatchability of eggs. Reasons for the decreasing DDE are discussed, especially the role of winter-feeding of eagles and the ban on the use of DDT in most Baltic countries.