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The Conservation Reserve Program and Grassland Birds

Results


We recorded 73 species of birds on the Conservation Reserve Program fields. Total densities (indicated pairs per 100 ha) were 123.5 in 1990 and 123.6 in 1991. Overall, the Lark Bunting was the most abundant bird in Program fields, although it was absent or rare in counties in the Drift Prairie and Black Prairie (Table 2). The Grasshopper Sparrow was the next most common species. The Red-winged Blackbird, third in average abundance, was uncommon in the more arid habitats of Montana and Butte County, South Dakota. The Western Meadowlark and Horned Lark, ranked fourth and fifth, showed patterns of abundance decreasing from west to east. Among the other species common in the fields, the Eastern Kingbird, Barn Swallow, and Mourning Dove occurred fairly regularly with average densities not varying markedly by county (Table 2). The Western Kingbird was most common in the Missouri Coteau and Drift Prairie; it was uncommon in the Black Prairie. The remaining species were far more variable, having high densities in some counties and being absent from others.

Table 1.  Densities of breeding birds (indicated pairs/100 ha) in cropland and in Conservation Reserve Program fields, and trends in abundance estimated from Breeding Bird Surveys.
Species Average density Average annual change (percent)a
Cropland CRP fields Central Region Continental
1990 1991
Lark Bunting (Calamospiza melanocorys) 4.2 23.1 21.8 -4.22 3 down arrows -4.17 3 down arrows
Grasshopper Sparrow (Ammodramus savannarum) 0.5 21.9 20.4 -4.58 3 down arrows -4.47 3 down arrows
Red-winged Blackbird (Agelaius phoeniceus) 1.1 13.4 19.3 -0.04 -0.88
Western Meadowlark (Sturnella neglecta) 4.3 8.4 7.3 -0.34 -0.72
Horned Lark (Eremophila alpestris) 18.0 9.1 5.5 -0.15 -0.62
Savannah Sparrow (Passerculus sandwichensis) 1.9 6.8 5.4 0.63 -0.63
Brown-headed Cowbird (Molothrus ater) 2.7 4.1 6.9 -0.26 -0.87 down arrow
Clay-colored Sparrow (Spizella pallida) 0 3.8 5.1 -2.08 down arrow -1.53 2 down arrows
Bobolink (Dolichonyx oryzivorus) 1.2 3.4 5.1 -2.74 3 down arrows -0.95
Common Yellowthroat (Geothlypia trichas) 0 2.2 4.4 -0.32 -0.38
Sedge Wren (Cistothorus platensis) 0 3.0 2.1 -0.97 1.31
Chestnut-collared Longspur (Calcarius ornatus) 5.0 3.0 1.6 -0.47 0.38
Eastern Kingbird (Tyrannus tyrannus) 0.2 1.9 2.2 0.43 -0.08
Western Kingbird (Tyrannus verticalis) 0.3 1.8 1.9 1.82 3 up arrows 1.59 3 up arrows
Barn Swallow (Hirundo rustica) 0.3 2.0 1.6 2.49 3 up arrows 0.98 2 up arrows
Mourning Dove (Zenaida macroura) 1.3 1.9 1.5 -0.07 0.06
Dickcissel (Spiza americana) 0.2 1.9 1.4 -1.44 2 down arrows -1.61 2 down arrows
Baird's Sparrow (Ammodramus bairdii) 0 1.6 1.7 -2.58 2 down arrows -1.90 down arrow
Vesper Sparrow (Pooecetes gramineus) 1.2 0.6 0.8 0.24 -0.85
Killdeer (Charadrius vociferus) 1.1 0.4 0.5 0.25 0.27
a down arrow decreasing (up arrow increasing) at P < 0.10;  2 down arrows (2 up arrows) at P < 0.05;  3 down arrows (3 up arrows) at P < 0.01.

For a comparison with cropland bird populations, we examined the original data from the Stewart and Kantrud (1972 ) survey, which provided information on 194 cropland fields totaling 4400 ha. Only the Horned Lark occurred in appreciably higher densities in cropland than in Conservation Reserve Program land, and the Chestnut-collared Longspur, Vesper Sparrow, and Killdeer were slightly more common in cropland (Table 1). In contrast, densities of the other 16 species listed were seven times greater (the median) in Program fields than in cropland.

Table 2.  Average density of breeding birds (indicated pairs/100 ha) in Conservation Reserve Program fields, by county, 1990-1991 average.
Species Great Plains Roughlands Missouri Coteau Drift Prairie Black Prairie Averagea
Fallon
MT
Butte
SD
Hettinger
ND
Sheridan
MT
Kidder
ND
McPherson
SD
Eddy
ND
Day
ND
Grant
ND
Lark Bunting 22.1 34.3 53.3 56.0 9.6 18.6 0.1 0 0 22.4
Grasshopper Sparrow 11.8 9.9 27.1 22.8 18.4 37.5 34.3 17.8 9.4 21.2
Red-winged Blackbird 0.8 2.1 22.1 4.3 25.4 25.8 18.7 32.6 18.7 16.4
Western Meadowlark 12.8 13.2 9.0 7.4 6.8 8.2 6.0 3.3 1.3 7.8
Horned Lark 10.1 20.0 6.7 15.2 3.4 4.8 2.4 0.5 0.1 7.3
Savannah Sparrow 0.1 0.4 9.2 4.6 5.7 2.8 8.0 14.1 11.9 6.1
Brown-headed Cowbird 1.7 0.6 8.1 11.8 5.3 8.3 6.1 5.0 1.2 5.5
Clay-colored Sparrow 0 0 0.5 6.4 2.2 2.1 12.0 12.4 6.7 4.5
Bobolink 0 0.1 5.1 1.5 2.5 1.6 5.5 9.7 15.6 4.2
Common Yellowthroat 0 0 0.4 0.2 1.9 1.8 3.3 12.6 13.6 3.3
Sedge Wren 0 0 0 0 0.2 0 0.7 9.6 17.0 2.6
Chestnut-collared Longspur 0 1.1 3.1 9.8 2.5 3.8 0 0.1 0 2.3
Eastern Kingbird 1.0 0.8 1.5 1.9 3.1 2.5 3.5 2.4 1.4 2.1
Western Kingbird 0.6 0.4 1.1 1.4 4.6 4.4 1.7 1.7 0.1 1.8
Barn Swallow 1.7 1.4 1.0 0.7 1.4 1.9 1.9 3.0 4.0 1.8
Mourning Dove 2.0 1.0 2.8 0.6 1.6 4.0 1.8 0.7 0.5 1.7
Dickcissel 0 0 0 0 0.4 1.3 0.3 10.7 4.1 1.6
Baird's Sparrow 0.5 1.1 0.1 9.2 1.3 1.2 0.7 0.5 0 1.6
a Weighted by area surveyed within each county.

We examined the population trends of these species, using the 1966-1990 data from Breeding Bird Surveys. Of the four species that occurred in higher densities in cropland than in Conservation Reserve Program fields, none had a significant (P < 0.10) upward or downward trend (Table 1). Six of the species less common in cropland than Program fields had significant downward trends. The two most common species in Program fields, the Lark Bunting and Grasshopper Sparrow, declined by more than 4 percent per year during 1966-1990, both in the Central Region and continentally (Table 1). The Clay-colored Sparrow also declined significantly in the Central Region and continentally. The Bobolink had been declining at 2.7 percent per year in the Central Region, and the Dickcissel at about 1.5 percent per year. Baird's Sparrow, a prairie species with a restricted range, had been declining at 2 percent per year.


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