Male Brown-headed Cowbird Attacks and Kills a Nestling

I observed a male Brown-headed Cowbird (Molothrus ater) attack and kill a nestling of an unidentified passerine in a grassland field in Day County, South Dakota, in June 2000. The killing or removal of nestlings by female cowbirds has been reported by others, but this behavior has not been documented previously in male cowbirds. Received 8 October 2002, accepted 3 March 2003. Female Brown-headed Cowbirds (Molothrus ater) often remove and sometimes eat host eggs (e.g., Scott et al. 1992). Female cowbirds have been observed attacking, removing, or killing nestlings (Du Bois 1956, Tate 1967, Beane and Alford 1990, Scott and McKinney 1994, Sheppard 1996), and recent technological advances in videography have provided evidence that this behavior may be more common than previously believed (Averill-Murray et al. 1999, Elliott 1999, Thompson et al. 1999, Pietz and Granfors 2000, Granfors et al. 2001, Stake and Cavanagh 2001). In some cases, female cowbirds have been observed destroying or removing entire host clutches or broods (e.g., Beane and Alford 1990, Scott and McKinney 1994, Elliott 1999, Granfors et al. 2001, Stake and Cavanagh 2001, pers.