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Contributions of the Conservation Reserve Program to Populations of Breeding Birds in North Dakota

Results


Of the 18 species that occurred commonly in CRP or cropland fields, 12 were more common in CRP fields than in cropland (Table 1). One, the Sedge Wren, occurred only in CRP. Six of the species that favored CRP habitat had suffered significant (P < O.1) population declines; the Grasshopper Sparrow and Lark Bunting, for example, each declined by about two-thirds during 1967-90. The Mourning Dove, an edge species, was nearly equally common in the two habitat types. Species more common in cropland than in CRP were Horned Lark, Vesper Sparrow, Upland Sandpiper, Chestnut- collared Longspur, and Killdeer, species that tend to avoid the taller and denser vegetation in CRP fields. None of those five species nor the Mourning Dove had exhibited population declines during 1967-90.

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.


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