Wheat seeds treated with heptachlor to control wireworms (Ctenicara pruinina) resulted in American kestrels (Falco sparverius) in the Columbia Basin accumulating residues of heptachlor epoxide (HE) that reduced productivity and caused some adult mortality. The kestrel is more sensitive to HE residues in eggs than the Canada goose (Branta canadensis moffitti), i.e., reduced productivity occurs at > 1.5 ppm in kestrel eggs vs. > 10 ppm in Canada goose eggs. Neither kestrel eggshells nor Canada goose eggshells were thinned by HE. The reduced use of heptachlor in 1979, because of a partial ban, resulted in an immediate lowering of HE concentrations in kestrel eggs the following year.
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Effects of heptachlor on American kestrels in the Columbia Basin, Oregon