As the percentage of grassland in a landscape increases, so does the success of duck nests (Reynolds et al. 2000). This relationship, while accounting for a relatively small percentage of the total variation in nest success, is nonetheless statistically significant for five duck species in the PPR. However, as with wetlands, the distribution of grassland is not uniform within the PPR. Because most soils in the Missouri and Prairie Coteau are rocky and the topography is rolling, much of this physiographic region is devoted to livestock production (pasture and hayland), and significant areas of native grassland remain. Consistent with the relationship between grassland area and nest success, duck nest success in the Coteau appears to be relatively high. In contrast, prior to 1985 the Drift Plain of the Dakotas, like most of Minnesota and Iowa, was dominated by cropland and contained very little grassland. Duck nest success in many places was distressingly low -- below the threshold necessary to sustain duck populations. That changed with the 1985 Farm Bill and the CRP.
CRP was authorized as a program to reduce soil loss on highly erodible land, reduce crop surpluses, and improve wildlife habitat. Under the program, farmers could apply for enrollment in CRP and, if accepted, were obligated to plant perennial cover in exchange for an annual payment. Most contracts were for 10 years. By 1985, it was widely recognized that inadequate grassland habitat was responsible for low duck nest success. Because of the potential for CRP to restore grasslands in the PPR, conservationists worked to persuade the U.S. Department of Agriculture to designate the entire PPR as a Conservation Priority Area due to its wildlife, and particularly, waterfowl values. This designation made nearly all previously cropped land in the PPR eligible for CRP, regardless of soil erodibility. Subsequent modifications to the implementation rules and scoring of CRP afforded advantages to farmers who were willing to restore wetlands and plant cover that was beneficial to wildlife.
Fig. 2. Duck productivity, expressed as July broods/100 ducks observed in the May survey.
By any measure, CRP was a huge success for waterfowl conservation. About 1.9 million ha of former cropland, 7% of the land base in the U.S. PPR, was enrolled in CRP. When water returned to the region in 1993, ducks responded. Duck nest success in CRP exceeded rates reported in earlier studies, and CRP had the added benefit of increasing the nest success in nearby Waterfowl Production Areas (Reynolds et al. 2000). Research on the effects of CRP concluded that duck nest success increased 46% as a result of CRP, and that CRP resulted in an additional 10.5 million ducks recruited into the fall population during 1992-97 (Reynolds et al. 2000). The weight of the evidence indicates that ducks will readily accept planted cover in which to nest and, given an adequate amount of cover in the landscape, can achieve nest success rates adequate to increase duck populations.
Clearly a focus of our conservation efforts must be the maintenance and expansion of cover programs such as CRP in the U.S. Unfortunately Canada does not have a similar program and much of the Canadian PPR, particularly in Saskatchewan, remains intensively cropped. Therefore the implementation of a similar, aggressive, extensive cover program in Canada is needed.
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