By Harold Kantrud, Rolf Koford, Douglas Johnson, and Michael Schwartz
The authors were all biologists at the Northern Prairie Wildlife Research Center, Jamestown, ND, when this article was written.
North Dakota Outdoors August 1993
These changes are the result of the U.S. Department of Agriculture's Conservation Reserve Program under the Food Security Act of 1985. By this program, USDA leased highly erodible cropland for 10 years if landowners established and maintained stands of perennial vegetation and agreed to leave the land idle for the length of the lease. The CRP particularly benefitted migratory birds. To many birds, the perennial vegetation on those highly erodible acres means "home" in the form of added breeding habitat.
The CRP was established primarily to bring crop production more in line with demand and to conserve and improve soil and water quality. The emphasis was on reduction of soil erosion and stream sedimentation and on improvement of water quality on erodible or eroding lands and tilled wetlands.
Another objective was to enhance wildlife habitat. Because the program has a target of restoring permanent cover on as many as 45 million acres nationwide, it presents enormous potential benefits for wildlife. North Dakota farmers found CRP especially attractive, and enrolled 2.88 million acres or about 10 percent of the state's cropland.
The Agricultural Stabilization and Conservation Service, which administers the program, offered landowners the choice of 14 different land uses under the 1985 Act. Most North Dakota farmers opted for tame grass plantings. Nationwide, tame and native grass plantings were about 82 percent of the total enrolled area during the first nine sign-up periods.
CRP distribution across the state generally reflects the distribution of highly erodible lands and tilled wetlands. Eddy, Hettinger and Kidder counties have the greatest percentages of area in CRP, whereas Stutsman, McHenry and Kidder counties have the greatest amounts of enrolled land. At the other extreme, Traill, Cass and Cavalier counties have the lowest percentages of enrolled land, and Traill, Oliver and Cass counties have the fewest acres.
CRP Acreage by County
To determine, in part, the degree to which wildlife benefits from CRP land, the U.S. Fish and Wildlife Service's Northern Prairie Wildlife Research Center is conducting studies on game and nongame species of breeding birds. Since 1989, biologists of the NPWRC, South Dakota State University, and the USFWS's Habitat and Population Evaluation Team in Bismarck have studied nest success of ducks on CRP land. In three studies nest searches were conducted on more than 5,000 acres of CRP land in Minnesota, North Dakota and South Dakota. In areas with many wetlands, CRP fields of tame grasses provide nesting cover for upland-nesting ducks. This type of cover is at least as secure as similar vegetative covers on federal waterfowl production areas.
Nest success and use of the fields by ducks varies greatly, however. All major species of upland-nesting ducks in the region - blue-winged teal, mallards, gadwalls, northern pintails, northern shovelers, green-winged teal and American wigeon - nest in CRP fields. Nest success of mallards, northern pintails and gadwalls, species that often nest relatively long distances from water, seems especially high in CRP fields.
Because these studies revealed that a combination of prairie wetlands and abundant nesting cover can result in high nest success, wetland restoration near tracts of CRP land may significantly increase waterfowl production. The CRP tracts must be carefully selected, however, and vegetation on associated wetlands must be properly managed to maintain a ratio of emergent cover to open water that attracts breeding pairs and provides good brood-rearing habitat.
In our study of waterfowl, broods of sharp-tailed grouse, ring-necked pheasants and gray partridge were also noted. Twenty-seven broods were observed in CRP fields, but only five broods in about the same area of WPAs. The great increase in harvest of ringnecked pheasants in North Dakota during the last few years is probably a major benefit of the program to hunters.
Biologists also noted several years ago that prairie chickens were establishing dancing grounds on CRP fields in Minnesota. CRP thus may provide an opportunity to restore populations of this formerly abundant bird.
During the studies of nesting ducks, biologists also found nests of large nongame birds such as short-eared owls, American bitterns and northern harriers. In 1990, NPWRC initiated a more extensive survey of the use of CRP fields by breeding birds in North Dakota, eastern Montana, South Dakota and western Minnesota. These four states have about 9.9 million acres of land enrolled in the program.
Biologists surveyed birds on 11,500 acres in 240 fields in 1990 and on 15,273 acres in 335 fields in 1991. Seventy-three species of birds were identified in these fields. Overall densities averaged 50 pairs/lO0 acres, and ranged from a high of 77 pairs/100 acres in1991 in Sheridan County, Montana, to a low of 19.5 pairs/100 acres in Fallon County, Montana,in1990.
The most common species on CRP fields have:the greatest potential of benefitting from the program. Many of these species, including bobolinks, lark buntings, grasshopper sparrows and dickcissels, are neotropical migrants - birds that summer in North America but migrate to Central or South America for the winter. These birds are the target of conservation by Partners in Flight - Aves de las Americas - a joint effort of states, private organizations and federal Agencies that began because of concern over population declines of many of these species.
A comparison of densities of common species in CRP fields with densities in cropland revealed that most grassland species were more common in CRP fields than in cropland. Conversion of cropland to perennial cover thus added suitable breeding habitat for these species and may enhance their populations. This change is especially important because during the last quarter-century several grassland species suffered major population declines in the central United States.
The declines were especially severe for lark buntings and grasshopper sparrows, which declined by more than 50 percent since the mid-1960s. These two species are, fortuitously, by far the most abundant nesting species in CRP fields.
Northern Prairie Wildlife Research Center biologists are also investigating the productivity of songbirds inhabiting CRP fields and alternative habitats in south-eastern North Dakota and west central Minnesota. Birds must not only occupy a habitat but also successfully raise young to maintain their population levels. Early indications are that only a quarter of the clutches hatch, but that nest success is quite variable. Because of this variability, further study is needed to determine whether nest success in CRP fields is as good as in alternative habitats.
The study of productivity in songbirds also includes an examination of rates of brood parasitism. The northern Great Plains is the center of distribution of the brown-headed cowbird. This species does not build a nest, but lays its eggs in the nest of a host species and leaves them for the host to incubate and to feed and protect the nestlings. Brood parasitism can reduce the nest success and the number of the host's fledged young.
The overall rate of parasitism was half as high in CRP fields as in WPA fields, suggesting that some feature of CRP fields reduces parasitism by cowbirds. Thus, CRP may have the potential of reducing the harm from parasitism across broad regions of the prairies.
Our study of waterfowl is complete and the results are being published in the Journal of Soil and Water Conservation. Because of annual variability in populations of grassland birds, biologists at NPWRC will continue to study nongame species for several years. The habitats in CRP fields will mature during those years and permit an assessment of the longer-term effects of the program.
Northern Prairie Wildlife Research Center is also initiating investigations of the effects of habitat fragmentation on ducks and songbirds that nest in grassland. Most nesting habitat of these species consists of islands of grassland in a vast sea of cropland. The effects of this fragmented habitat on species composition and reproduction are virtually unknown but probably harmful. The many CRP fields of widely varying size offer a good opportunity to examine the effects of field size and isolation on use and reproduction by birds.
Although more research on habitats provided by CRP in the northern Great Plains is needed, early results indicate the tremendous value of restored grasslands to a host of birds that breed in the prairies. The 10-year leases under CRP begin to expire in l996. At that time, landowners can return their land to cultivation. Whether or not they will do so depends on available alternatives.
Although many farmers have not yet reached a decision, most of those polled in a recent survey in North Dakota intend to return their CRP fields to cultivation. Continuing the CRP in some form will offer valuable conservation of soil and water and will maintain important habitats for a wide variety of birds.
Population trends of birds that breed in cropland or CRP fields, as determined from Breeding Bird Surveys during 1966-90, in the central region of the United States between the Rocky Mountains and the Mississippi River. Species are listed in order of decreasing abundance within groups.
Summary of Nongame Bird Research
Other Related WWW Reports