Brown-headed cowbirds ranked sixth in total abundance among all species present. Recent alterations of the landscape coupled with great changes in the physical make-up of the habitats has had a positive impact on this species. The largest breeding density in our study area occurred in shelterbelts where the population was nearly four times larger than in the second ranking habitat which was natural wetland vegetation. As is typical of most Icterids, this species demonstrated the ability to adapt to gross changes in the habitat base and to successfully exploit and flourish in the newly formed habitat. Evidence obtained at nest sites indicate that brown-headed cowbirds actively pierce and remove the eggs of their host.
Some hosts do likewise, or they cover the cowbird eggs with additional nest material.
In several cases, we have recorded nest abandonment by the host species after their nest was parasitized.