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The effects of in ovo and early post-hatch DDT expourse on American robins from the Okanagan Valley, British Columbia Smith, Lori Kim

Abstract

American robin (Turdus migratorius) eggs from orchard areas of the Okanagan Valley, British Columbia contain high levels of dichlorodiphenyltrichloroethane (DDT) and its metabolites. These contaminants are present in the soil as a result of heavy historical use. DDTs accumulate in the earthworms that live in the soil and are passed to the robins through their preference for earthworms as a food source during the breeding season. These chemicals are then passed to the offspring via the egg yolk and in the diet. Despite the high residue levels found in these robins, no impairments in their reproductive success have been found. In order to assess more subtle and/or long term effects of DDTs on a variety of parameters, ten-day old nestlings were collected from the Okanagan, along with controls from the Lower Mainland of British Columbia, and raised and bred in captivity. Eggs were collected in order to measure contaminant levels. Total DDTs in the Okanagan eggs ranged from 5.7 to 277.6 μ/g (mean 49.3 μ/g), whereas in the Lower Mainland eggs they ranged from 0.4 to 3.4 μ/g (mean 1.5 μ/g). Eggs collected from the Lower Mainland and Okanagan were of similar weights, lengths, and widths. Okanagan chicks collected in 1997 had significantly shorter middle toes than the other birds, and appeared to lag in their tarsus growth. As adults, these birds laid smaller eggs than the Lower Mainland controls, but showed no differences in the timing of their reproductive activities, their laying, hatching, and fledging success, or their reproductive behaviors. They demonstrated an increased susceptibility to infectious disease, lower corticosterone levels during the early phases of a restraint test, and enlarged hearts, livers, and kidneys. Although robins in the Okanagan continue to thrive and reproduce despite their high levels of contamination, DDT likely has the potential to influence several aspects of their lives, as evidenced by the many significant correlations with in ovo exposure. However, it remains that genetic differences between the Lower Mainland and Okanagan birds may account for many of the effects seen.

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