| Abstract
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In 2001, a federal program, the Conservation Reserve Enhancement Program (CREP), was initiated in 20 counties in south-central Pennsylvania to address soil erosion and water quality with an expected secondary benefit of providing habitat for wildlife. Because of the decline in grassland bird populations in North America I wanted to identify what species were using CREP fields. I also wanted to identify what field and landscape characteristics affected use and productivity of avian species on CREP fields. To assess the benefit of CREP fields benefit for grassland birds, I compared them to active hayfields. The project was conducted from May 2001--July 2004 in 9 CREP counties of south-central Pennsylvania. I randomly selected CREP fields in three size categories: 2.0--4.0 ha, 7.3--12 ha, and 16--28 ha to get a mixture of field sizes because small fields were much more common than either medium or large fields. Hayfields were located as near as possible to selected CREP fields. I surveyed birds in all fields twice during the breeding season, using distance sampling to generate densities for each species that had >25 observations. I searched for nests in over half the fields that were surveyed. Nests that were located were monitored until completion (fledging, depredation or abandonment). Vegetation was measured at the nest and along the survey transects. Landscape characteristics were calculated using geographic information system data for the areas surrounding the fields. I made a total 1,929 observations of 31 different species on 114 CREP fields. I monitored 969 nests of 19 species in 73 CREP fields. The most common species was the red-winged blackbird (Agelaius phoeniceus) with 1,052 observations and 613 nests. The next most common species were field sparrows (Spiza pusilla; 111 obs.; 171 nests), song sparrows (Melospiza melodia; 343 obs.; 78 nests) and indigo buntings (Passerina cyanea; 130 obs.; 21 nests). The most common grassland specialists were grasshopper sparrows (Ammodramus savannarum; 104 obs.; 19 nests) and eastern meadowlarks (Sturnella magna; 31 obs.; 9 nests). Ring-necked pheasants (Phasianus colchicus; 3 nests), dickcissels (Spiza americana; 2 obs.; 1 nest), Henslow's sparrows (Ammodramus henslowii; 2 obs.), savannah sparrows (Passerculus sandwichensis; 17 obs.; 2 nests), vesper sparrows (Pooecetes gramineus; 10 obs.; 5 nests) and bobolinks (Dolichonyx oryzivorus; 50 obs.; 1 nest) were uncommon to rare. Mayfield nest success for the most common above-ground nesting species, red-winged blackbird, was 30.2 ± 2.0% and the most common ground nesting species, grasshopper sparrow, was 12.4 ± 7.1%. I developed models to describe species density and nest abundance. Both field and landscape characteristics were significantly associated with species density and nest abundance, but the specific variables and the direction of effect varied among species and in some cases varied between density and nest abundance within a species. Consequently, there were no specific variables that were universally important to the community of birds using CREP fields. I made 68 observations of 7 different species on 16 hayfields and 185 observations of 8 different species on the 16 matched CREP fields. Species richness was higher (p=0.001) on CREP fields (2.75 ± 0.233) than hayfields (1.38 ± 0.24). Densities of field sparrows, song sparrows and indigo buntings were higher on CREP fields than hayfields (p = 0.012, 0.004, 0.006 respectively). No other species differed in density between hayfields and CREP fields. I located 193 nests of 10 different species on 15 CREP fields and 87 nests of 5 species on 15 hayfields. Species richness of nesting birds was higher (p< 0.001) on CREP fields (2.47 ± 0.40) than hayfields (0.60 ± 0.19). Field sparrow and song sparrow nest abundance was higher (p = 0.011, 0.001 respectively) on CREP fields (0.318 ± 0.15, 0.193 + 0.10) than hayfields (0.006 ± 0.01, 0.006 ± 0.01). No other species differed in nest abundance between hayfields and CREP fields. However, wild turkeys, indig buntings and eastern meadowlarks were only located nesting on CREP fields and not on hayfields. Nest success of red-winged blackbirds (the only species with multiple nests on hayfields) was higher (p = 0.029) on CREP fields (27.9 ± 6.2%, n = 59) than hayfields (12.6 ± 3.4%, n = 73). My study indicated that generalist and edge species used CREP fields much more than grassland specialists. Although numbers of grassland specialists are low, overall species richness, abundance and nest success were higher on CREP fields than hayfields. To provide habitat for a diversity of farmland and grassland species and to increase the likelihood that grassland specialists will use CREP fields, the largest fields possible should be enrolled in the CREP program. Since the sizes of agricultural fields in Pennsylvania tend to be small, one way to increase effective field size would be to attempt to enroll adjoining fields in CREP even if they are owned by different people. Fields should be managed to provide heterogeneous vegetation, including heterogeneity of vegetation types (e.g. forbs and grass), species and structure (e.g. different heights and density). Some form of maintenance, such as strip mowing, burning or light disking, on the field will probably be necessary to maintain or attain heterogeneity. Monitoring of CREP fields should continue to assess how avian species composition and abundance change as the fields mature.
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