Grassland bird communities on conservation and marginal grasslands in an agricultural landscape

• Generalists and short-grass species replaced tallgrass species on marginal lands.
• One grassland obligate species was frequently observed on marginal grasslands.
• Planting diversity was associated with species-specific effects on bird density.

Six years of point count data in eastern Nebraska and western Iowa, USA, were used to investigate how the community structure of grassland birds and the densities of four focal species (common yellowthroat, dickcissel, grasshopper sparrow and sedge wren) varied on conservation lands with differing management strategies (i.e., warm- versus cool-season grasses and low- to high-diversity plantings), and between conservation and unmanaged marginal grasslands (e.g., field borders and terraces). Model-selection results indicated that grasshopper sparrow and dickcissel densities were influenced by grassland type, with higher densities in parcels dominated by warm-season grasses. Species-specific changes in density in response to planting diversity reinforced the value of creating heterogeneous habitat for grassland birds. Densities for all four species were substantially lower in unmanaged marginal grasslands versus conservation parcels and the community structure between the two habitats differed significantly, with generalist species (e.g., American robins, common grackles and grassland species associated with shorter, sparse and patchy vegetation (e.g., horned lark and vesper sparrow)) largely replacing tallgrass specialists in unmanaged marginal grassland parcels.