Nelson's Sharp-tailed Sparrow Nest Parasitized by Brown-headed Cowbird

On 22 July 2004, we found a Nelson's Sharp-tailed Sparrow (Ammodramus nelsoni) nest in Sheridan County, Montana, containing a single Brown-headed Cowbird (Molothrus ater) nestling that was about to fledge. A punctured sharp-tailed sparrow egg was found below the nest. This is the second definitive report of cowbird brood parasitism of a Nelson's Sharp-tailed Sparrow nest and the first indicating successful rearing of a cowbird by this host species. The impact of cowbird parasitism on nesting success of Nelson's Sharp-tailed Sparrow has not been studied, but our record indicates that nest failure (i.e., producing no host young) may be an outcome for some nests of this species.