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Conservation Reserve Program and Migratory Birds in the Northern Great Plains


by
Douglas H. Johnson
National Biological Service
Rolf R. Koford
National Biological Service
U.S. Department of Agriculture programs have mediated supply and demand of commodities and maintained the agricultural industry, but several programs have also offered various kinds of conservation benefits. The 1985 Food Security Act (Farm Bill) featured the Conservation Reserve Program (CRP), which paid farmers to plant perennial cover on highly erodible lands and to leave this land intact for a 10-year contract period. During that period we conducted two studies to determine the value of CRP fields to breeding birds in the northern Great Plains.

Methods
In one investigation, we censused breeding birds on about 400 fields in nine counties in eastern Montana, North Dakota, South Dakota, and western Minnesota (Johnson and Schwartz 1993). These four states have about 4 million ha (9.9 million acres) of CRP land, which is nearly 30% of all land included in the program. Most of these CRP fields were planted to mixtures of native and introduced grasses and legumes. We compared the average estimated density of breeding pairs in CRP fields in North Dakota with the density in croplands in a random sample of quarter-sections surveyed in the state (see Igl and Johnson, this section). We believe this is an appropriate comparison because nearly all CRP lands would have been in cropland without the program. In addition, North Dakota is the only state with comparable information about bird populations in cropland. Results are available for 1992 and 1993.
In a second investigation, we examined daily survival rates of nests (eggs and young), a key component of reproductive success, on 11 CRP fields in North Dakota and Minnesota in 1991-93. For comparison with CRP fields, we also studied an alternative habitat with a similar breeding-bird community. We studied 11 idle grassland fields on upland parts of federal Waterfowl Production Areas (WPAs); their vegetation typically is planted to mixtures of legumes and to grasses.

Bird Populations and Reproductive Success
Seventy-three different species were counted in the first study; most of these species were far more common in CRP fields than in cropland (Table 1). Differences were especially great for several grassland species that had declined markedly in the Breeding Bird Survey's Central Region of North America between 1966 (when the surveys began) and 1990. For example, lark buntings (Calamospiza melanocorys) and grasshopper sparrows (Ammodramus savannarum), whose numbers fell by about two-thirds during that period, were about 10 and 16 times more common in CRP habitat than in cropland. Table 1. Densities (pairs per 100 ha) of most common birds in Conservation Reserve Program fields and in cropland fields in North Dakota, 1992-93, and trends from the Breeding Bird Survey for the Central Region of North America, 1966-90.
  CRP fields
 Cropland
  
Species
 		 1992 1993 1992 1993 Trend
 
Lark bunting (Calamospiza melanocorys) 24.54 9.14 2.01 1.28 -64.5
Red-winged blackbird (Agelaius phoeniceus) 21.50 10.90 1.86 0.90 -1.0
Grasshopper sparrow (Ammodramus savannarum) 21.14 10.21 1.33 0.58 -67.5
Savannah sparrow (Passerculus sandwichensis) 7.28 8.60 0.12 1.48 16.3
Brown-headed cowbird (Molothrus ater) 7.11 5.03 2.61 2.51 -6.1
Bobolink (Dolichonyx oryzivorus) 7.74 3.53 2.73 2.11 -48.7
Western meadowlark (Sturnella neglecta) 5.43 5.26 1.28 1.16 -7.8
Clay-colored sparrow (Spizella pallida) 5.07 3.63 0.02 0.02 -39.6
Common yellowthroat (Geothlypis trichas) 2.49 1.87 0.02 0.02 -7.4
Horned lark (Eremophila alpestris) 2.38 0.53 19.96 29.18 -3.5
Sedge wren (Cistothorus platensis) 0.73 1.13 0 0 -15.5
Dickcissel (Spiza americana) 1.37 0.03 0.19 0 -29.4
Baird's sparrow (Ammodramus bairdii) 0.26 0.68 0.34 0.02 -46.6
Upland sandpiper (Bartramia longicauda) 0.40 0.13 0.92 0.65 145.7
Chestnut-collared longspur (Calcarius ornatus) 0.02 0.03 11.38 2.08 -10.7
The most recent Breeding Bird Surveys indicate that these grassland species, which had been declining for a long time, appear to be increasing (Reynolds et al. 1994).
Overall, daily survival rates of nests were similar in CRP fields and WPA fields (Table 2). In North Dakota there was some indication that nests of grasshopper sparrows and western meadowlarks (Sturnella neglecta) had higher daily survival rates in CRP fields than in WPA fields. Differences between states and among years, however, make generalizing difficult. Predation caused 80% of the nest failures. Table 2. Daily survival rates of nests in Conservation Reserve Program fields and on Waterfowl Production Areas, North Dakota and Minnesota. Numbers of nests are in parentheses.
Species North Dakota
 Minnesota
  CRP WPA CRP WPA
American coot (Fulica americana) - - 0.92 (14) -
Blue-winged teal (Anas discors) - - 0.94 (19) 0.95 (34)
Bobolink (Dolichonyx oryzivorus) - - 0.92 (16) 0.93 (32)
Clay-colored sparrow (Spizella pallida) - 0.93 (49) - 0.97 (24)
Grasshopper sparrow (Ammodramus savannarum) 0.95 (39) 0.91 (14) 0.92 (13) -
Mallard (Anas platyrhynchos) 0.96 (20) - - 0.97 (10)
Red-winged blackbird (Agelaius phoeniceus) 0.92 (70) - 0.86 (25) -
Savannah sparrow (Passerculus sandwichensis) - - 0.86 (13) 0.95 (30)
Upland sandpiper (Bartramia longicauda) - 0.99 (19) - -
Western meadowlark (Sturnella neglecta) 0.95 (20) 0.87 (14) - -

Implications
These studies show that federal agricultural programs can have an enormous effect on wildlife resources over broad areas. In addition, with the restoration of suitable habitat, in this case mostly a mixture of introduced grasses and legumes rather than native prairie, populations of grassland birds can flourish. The similar daily survival rates of nests in CRP and WPA fields indicate that the habitat quality of CRP fields and WPA fields is roughly comparable.
More information is needed to provide a fuller picture of how the CRP is affecting trends in grassland birds. Information on temporal and spatial effects is especially useful. As CRP fields age, their attractiveness to certain species may change. Daily survival rates of nests also may change. Spatial effects are apparent in our censuses and undoubtedly exist on a wider scale. Finally, we need to integrate results from field studies with trend data from the Breeding Bird Survey.
For further information:
Douglas H. Johnson
National Biological Service
Northern Prairie Science Center
8711 37th St. SE
Jamestown, ND 58401
References
Johnson, D.H., and M.D. Schwartz. 1993. The Conservation Reserve Program and grassland birds. Conservation Biology 7:934-937.

 Reynolds, R.E., T.L. Shaffer, J.R. Sauer, and B.G. Peterjohn. 1994. Conservation Reserve Program: benefit for grassland birds in the northern plains. Transactions of the North American Wildlife and Natural Resources Conference 59:328-336.


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