A toxicological assessment of Peregrine Falcons, Falco peregrinus tundrius, breeding in the Keewatin District of the Northwest Territories, Canada

Abstract

Eggshell thinning, and organochlorine residues in egg contents, blood plasma of adults and young, and prey species, were determined for Peregrine Falcons (Falco peregrinus tundrius) nesting at Rankin Inlet, Northwest Territories, Canada. Shells from 78 eggs representing 62 clutches of 26 pairs from 1981-1986 averaged 16% thinner than eggs collected prior to the introduction of DDT, only 1% less than the thinning level considered critical for successful reproduction in this species. About 10% of all peregrine pairs to initiate a breeding attempt failed with egg breakages. Geometric mean levels of DDE residues in addled eggs from 36 nesting attempts and in 88 blood plasma samples from adults, were 7.6 ppm (wet weight) and 0.8 ppm (wet weight) respectively. Levels of DDE in blood plasma were positively correlated with DDE levels in the contents of eggs. DDE levels in the contents of eggs were negatively correlated with shell thickness. Residues of a number of other organochlorine pesticides and polychlorinated biphenyls were found in egg contents and in the plasma of adult birds. Only DDE was found in measurable quantities in the blood plasma of nestlings. Levels of organochlorines were often highly correlated in both plasma and egg samples, suggesting that peregrines are exposed to these compounds collectively. All but one of 11 prey species sampled showed measurable levels of organochlorines. Only one species, an insectivorous passerine, contained DDE residues high enough to potentially affect breeding success of peregrines in the study area, while one duck and two shorebird species were the only other prey species to show elevated DDE levels. Relatively low pesticide residues and high reproductive success of this population, however, are explainable through the low proportion of highly contaminated migratory prey species used by these birds on the breeding grounds. Additionally, asynchrony in the arrival times of peregrines and contaminated migratory prey species results in the use of relatively uncontaminated prey before laying. Recommendations are presented for future monitoring of pollution and population trends of tundra peregrines in Canada.