Northern Prairie Wildlife Research Center
Estimated numbers of breeding pairs in CRP fields, and in all habitats, for North Dakota in 1992 and 1993 demonstrate the extensive use of CRP by many species (Table 2). CRP composed only about 7% of the land in North Dakota but supported more than 20% of the statewide population of many species in one or both years. That percentage, averaged for the two years, was 26.6 for Sedge Wren, 22.9 for Savannah Sparrow, and 22.2 for Grasshopper Sparrow. At the other extreme, CRP supported only about 2.7% of Vesper Sparrows and 0.7% of Horned Larks in the state.
If we assume the return of CRP habitat to cropland and substitute densities of breeding birds in cropland for densities in CRP, we obtain a measure of the importance of CRP to each species (Table 3). Conversion of CRP to cropland would have reduced numbers of Sedge Wrens by 25.8%, Grasshopper Sparrows by 20.5%, and Savannah Sparrows by 18.8%. Conversely, numbers of Horned Larks and Vesper Sparrows would have risen by 9.7% and 2.3%, respectively.