Chapter 9: The ecology of brown-headed cowbirds and their effects on southwestern willow flycatchers

Abstract

Brown-headed cowbirds (Molothrus ater) are obligate brood-parasites, that is, female cowbirds lay their eggs in nests of other species. If the cowbird eggs are accepted, the host pair may raise the young cowbird, often at a reduction of the hosts' reproductive success. Cowbird females are also known to remove host eggs and nestlings from nests, which may also affect the reproductive success of the hosts (Smith 1981, Scott et al. 1992, Sealy 1992). It is difficult to assess the impact of parasitism both because reproductive success operates at many levels and because the hosts have defenses against parasitism or cowbird intrusion. In this chapter, we review the data on the effects of brood parasitism on reproductive success of the southwestern willow flycatchers (WIFL). We estimate the effects of brood parasitism on populations of WIFLs and the degree to which parasitism is a factor in their recovery. For most of the analyses, we use data from one population along the South Fork Kern River, Kern County, California.

Parent Publication

• Status, ecology, and conservation of the southwestern willow flycatcher

Citation

Uyehara, J. C.; Whitfield, Mary J.; Goldwasser, Lloyd. 2000. Chapter 9: The ecology of brown-headed cowbirds and their effects on southwestern willow flycatchers. In: Finch, Deborah M.; Stoleson, Scott H., eds. Status, ecology, and conservation of the Southwestern Willow Flycatcher. Gen. Tech. Rep. RMRS-GTR-60. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 95-106.