Effects of Heptachlor on American Kestrels in the Columbia Basin, Oregon

Abstract

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. J. WILDL. MANAGE. 47(4):1080-1087 The history of heptachlor as a wheat seed treatment to control wireworms in Umatilla and Morrow counties, Oregon, is poorly understood. Through 1970, it was listed in the Pacific Northwest Insect Control Handbook (Anon., various dates) after aldrin and dieldrin with an application rate on seed of 1 oz/bushel. It was not listed in 1971, 1972, and 1973. Then from 1974 to date, heptachlor was listed at 2 oz/bushel (=2,000 ppm). In 1976 and 1977, die-offs of several species of birds occurred in Umatilla and Morrow counties, Oregon. Residues of heptachlor epoxide (HE) that are considered lethal (Stickel et al. 1979) were found in brains of ring-necked pheasants (Phasianus colchicus), black-billed magpies (Pica pica), California quail (Callipepla californica), Canada geese, and a golden eagle (Aquila chrysaetos) (Blus et al. 1979). This history of wildlife mortality associated with heptachlor prompted a detailed study of the Canada goose population nesting on the Umatilla National Wildlife Refuge (NWR) (Blus et al. 1979). HE in eggs was correlated with hatching success; 95% of the nests in which sample eggs contained ?:1 ppm HE were successful compared with only 20% of those with eggs that contained >10 ppm. The source of HE in geese appeared to be ingestion of seeds treated with heptachlor for wireworm control. The present study involving the American kestrel was designed to complement the Canada goose investigation. We reasoned that Canada geese were obtaining heptachlor directly from the ingestion of treated seeds; however, if American kestrels obtained heptachlor, it would indicate that residues moved through food chains. American kestrels eat mostly insects, especially grasshoppers, but also mice, small birds, and some lizards and amphibians (Brown and Amadon 1968). Biological technicians collecting field data for this study included B. E. Foreman, G. A. Green, R. A. Grove, K. D. Hansen, E. G. Huff, and R. R. Sheehy. C. M. Bunck provided statistical assistance. J. E. Kurtz and G. M. Constantino, refuge managers at Umatilla NWR, kindly allowed use of the refuge facilities.