Host-parasite Relationships of the Brown-headed Cowbird in a Prairie Habitat of West-central Kansas

The parasitic nature of the Brown-headed Cowbird (Molothrus ater) is believed to have developed as a result of its association with the bison (Bison bison). Cowbirds subsisted on insects flushed by herds of bison, however, the nomadic nature of the bison made it impossible for cowbirds to remain with the herd and simultaneously perform nesting activities. Theoretically the evolution of parasitic habits allowed the cowbird to achieve reproductive success and concurrently maintain the established feeding relationship with the bison. Thus the distribution of the cowbird was similar to that of the bison or as Friedmann (1929) states, “the home of the cowbird was the open grasslands of the midcontinent.” Therefore the reproductive success of the cowbird was determined by the establishment of a functional equilibrium of a host-parasite relationship in a prairie habitat. In this regard, Sutton (1967) states that possible ground-nesting hosts in open grassland in Oklahoma are not heavily parasitized. Mayfield (1965) states that host species of the cowbird in western grassland have had long ancestral experience with parasitism and are much less receptive than host species of the eastern forest which have little experience with the social parasite. Data from breeding bird surveys, Van Velzen (1972) show that the center of abundance of the cowbird is still within the central plains of the United States. This suggests that species nestin g in these predominantly grassland states are receptive hosts. The purpose of this paper is to present data on the extent of cowbird parasitism and to discuss adaptations to parasitism of hosts nesting in a predominantly prairie habitat.