The Impact of CRP on Avian Wildlife: A Review

We reviewed the literature to assess the impact of the Conservation Reserve Program (CRP) on bird populations in the central USA. The CRP replaced production agriculture fields with grassland habitat used by more than 90 species of birds. At least 42 bird species nested in CRP habitats. Bird species richness in CRP fields was similar to that in rowcrop fields, but relative abundance was 1.4 to 10. 5 times higher in CRP plantings. Nest abundance was 13.5 times higher in CRP than crop fields, although nesting success of songbirds was only slightly higher in CRP fields (40% vs. 36% in crops). Limited evidence suggests that the CRP has positively affected the population growth rates of several nongame grassland bird species. Waterfowl nest densities and nesting success in CRP fields were similar to those occurring in grassland habitats managed specifically for waterfowl. The presence of CRP grassland has been postulated to have improved the quality of existing duck nest habitat by dispersing nests over a larger area. Ring-necked pheasant (Phasianus colchicus L.) populations seemingly increased substantially with CRP acres. Little evidence of positive population response by northern bobwhites (Colinus virginiunus L.) to the CRP is available. Overall, grassland birds known to be declining throughout North America were seemingly the most benefitted by the CRP. Research QuestionsA secondary objective of the Conservation Reserve Program (CRP) was the creation of fish and wildlife habitat. Wildlife conservationists predicted substantial benefits for grassland birds. Our objective was to review the literature evidence of the impact of CRP on grassland bird populations. Literature SummarySeveral studies have recently been published on wildlife use of CRP fields. No integrated review of the evidence of CRP impacts on wildlife populations is available. Study DescriptionWe reviewed the research literature for quantitative data on grassland bird occurrence (species richness) and abundance and reproductive success in CRP plantings in the central USA. We limited our review to the breeding season because of a paucity of data on winter use of CRP by birds. Applied QuestionsDoes the CRP contribute sufficiently to grassland bird populations to justify CRP (or similar) provisions in future federal farm legislation on wildlife conservation grounds? In the central USA, more than 90 bird species were documented using CRP plantings during summer breeding periods, with direct evidence of nesting by more than 40 species. Direct comparisons of crop and CRP fields revealed no differences in total number of species occurring in the two habitat types. But CRP fields supported from 1.4 to 10.5 times the number of individual birds as did crop fields. Nest abundance was from 8.8 to 27 times higher in CRP fields than in crop fields. Nest success of songbirds was slightly higher in CRP fields (40%) than in crop fields (36%). Overall, CRP fields produced about 14 times as many songbirds as did rowcrop fields. Several assessments suggest nongame bird populations increased because of the CRP. Duck nesting in cropfields is uncommon. Duck nest densities in CRP fields were similar to those occurring in habitats managed for waterfowl. Duck nest success in CRP fields was equal to or higher than that on lands managed by public agencies for waterfowl. Ring-necked pheasant numbers were three to five times higher after CRP plantings were established. The success of pheasants nesting in CRP fields was greater than that necessary for population growth. Although use of CRP land by northern bobwhites was substantial, direct evidence of CRP habitat contributing to quail population growth was lacking. Overall, the CRP provides high-quality breeding habitat for many grassland birds, including several that have been undergoing long-term population declines (e.g., grasshopper sparrow, bobolink, Baird's sparrow, Henslow's sparrow, field sparrow, lark bunting, clay-colored sparrow, ring-necked pheasant, northern bobwhite, mallard, gadwall). Grassland bird response to the CRP seemingly is sufficient to justify efforts to maintain long-term farm set-aside provisions in future federal farm legislation based on wildlife conservation benefits.