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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	-4.17
Grasshopper Sparrow (Ammodramus savannarum)	0.5	21.9	20.4	-4.58	-4.47
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
Clay-colored Sparrow (Spizella pallida)	0	3.8	5.1	-2.08	-1.53
Bobolink (Dolichonyx oryzivorus)	1.2	3.4	5.1	-2.74	-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	1.59
Barn Swallow (Hirundo rustica)	0.3	2.0	1.6	2.49	0.98
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	-1.61
Baird's Sparrow (Ammodramus bairdii)	0	1.6	1.7	-2.58	-1.90
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 decreasing ( increasing) at P < 0.10;  () at P < 0.05;  () 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.

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.