A recent study failed to show population-level effects of cowbird parasitism on host species and refuted key predictions about impact of parasitism. Rates of parasitism depend on the proximity of cowbird feeding sites to host breeding sites. Rates of parasitism sometimes correlate poorly with numbers of cowbirds counted in an area. Trapping is seen as the most efficient tool for removing large numbers of cowbirds. Cowbird control is controversial.
Scientists suggest there is little evidence that cowbirds have population-level impacts on hosts.
Further, they point out that control has limited impact on reducing parasitism on a broad geographic scale. Traps must be located where cowbirds congregate, like in feeding areas, and trapping appears to reduce parasitism mostly near such trap locations. The farther hosts are from the traps, the less likely they will benefit from control. Cowbird control is expensive. Cowbird control programs have proceeded without a general framework, with little coordination between programs, or between the land management and scientific communities.