Long-term investigation of the degree of exposure of German peregrine falcons (Falco peregrinus) to damaging chemicals from the environment

Abstract

The contamination of German peregrine falcons (Falco peregrinus) with organochlorine (CHC) biocides and mercury (Hg) was investigated over the years 1955–2002. A total of 960 unhatched eggs from eastern Germany, Baden-Wurttemberg (BW) and North Rhine-Westphalia/Rhineland Palatinate (NRW/RP) were analysed for the biocides DDE, HCB, PCB, etc., and for shell index and shell thickness. Hg analyses from 367 samples (unhatched eggs, moulted and nestling feathers, tissue samples) complete the investigation. The results confirm that the collapse of the German peregrine populations is correlated with the application of the insecticide DDT. The mean DDE values in BW over the years 1970–1976 were above the relevant threshold values of 70–100 μg/g (all concentrations refer to the dry sample mass), with single analyses showing values above 100 μg/g until as late as 1987. The mean contamination levels in the 1960s can be retrospectively assumed to have lain above 200 μg/g. With the help of thorough conservation measures it was possible after a fall in numbers of about 80% to stabilise the remnant population in BW . Following the West German DDT ban in 1972 and the resulting decline in environmental CHC contamination, this core population was able to recover from about 1980 onwards and has since increased tenfold. The shell index improved steadily from 1.48 (1970–1971) to a normal value of 1.80–1.88 (2000–2002). Hg contamination in western Germany stayed under toxic threshold values over the period 1969–1991. The significantly more intense application of DDT in eastern Germany, continuing until 1989, led to the extinction of the peregrine falcon, of both the cliff- and tree-nesting populations. This phenomenon is described with respect to DDE analysis data and shell thickness/index studies, complemented by observations of breeding biology. In addition, the employment in the GDR of methyl/phenyl Hg as seed treatments had dramatic local toxic effects on embryo survival and shell thickness. Hg burdens reached very high levels in feathers (147 µg/g) and eggs (65 μg/g). The combination of DDT and Hg was responsible for the species’ extinction in this region. The current peregrine falcon population of eastern Germany even now shows biocide contaminant burdens up to 3 times higher than in samples from western German falcons. Shell index and shell thickness had, however, normalised to a large extent by 2002. The tree-nesting habit of the peregrines formerly breeding in the forested lowlands of Central and Eastern Europe, a tradition which had been passed on by imprinting, has been completely eradicated as a result of the effects of the environmental contamination. In NRW/RP unhatched eggs over the period 1989–2002 show uncritical DDE contamination levels in the region of 4–20 μg/g with normal shell index values. PCB analyses from all three regions confirm the highest levels of contamination from industrial centres with no clear trend so far. HCB burdens peaked at a maximum of 80 μg/g and have been stable at <1 μg/g since 1983. Population parameters did not improve in BW until 1976, after DDE and HCB contamination levels had started to decrease as a result of the bans on use. In East Germany and NRW/RP, the documented recolonisation and increases in breeding success parameters were only possible after the DDE levels (and in East Germany additionally the Hg levels) had fallen to below toxic threshold levels.