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The Nesting, Reproductive Performance, and Chlorinated Hydrocarbon Residues in the Red-Tailed Hawk and Great Horned Owl in South-Central Montana

John C. Seidensticker IV and Harry V. Reynolds III
The Wilson Bulletin
Vol. 83, No. 4 (Dec., 1971), pp. 408-418
Stable URL: http://www.jstor.org/stable/4160137
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Nesting, Reproductive Performance, and Chlorinated Hydrocarbon Residues in the Red-Tailed Hawk and Great Horned Owl in South-Central Montana
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Abstract

We report on the nesting and reproductive performance of the Red-tailed Hawk and Great Horned Owl in south-central Montana during 1966 and 1967. Hawk and owl breeding seasons spanned 105 and 125 days respectively in 1967. Great Horned Owls wintered on the study area, but at least some Red-tailed Hawks winter south of the study area. Both hawks and owls nested primarily in cottonwood trees. The clutch size and number fledged from successful nests of Red-tailed Hawks averaged 2.9 and 1.7 respectively while Great Horned Owl clutch size and number fledged per successful nest averaged 2.2 and 1.8 respectively. The number of young fledged per recorded nesting attempt averaged 0.9 for the hawk and 1.2 for the owl. Nesting success for the hawk was 50 per cent and 64 per cent for the owl. All tissue and eggs contained measurable but relatively low levels of DDE, DDT, DDD, and dieldrin, and some samples contained heptachlor epoxide. The one hawk and one owl egg analyzed contained PCBs. The Great Horned Owl did not have thin eggshells but we did find thinning in Red-tailed Hawk eggshells.

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