Grassland bird response to enhanced vegetation diversity in restoration plantings in the Spring Run Complex of northwestern Iowa

Loss of habitat is one of the primary factors affecting population declines of grassland birds, and recovery efforts have focused on increasing the amount of grassland habitat in the landscape. Assessing the value of habitat restorations for grassland birds is an essential component of grassland bird conservation. We compared grassland bird habitat use, reproductive success, nestling growth rates, nestling baseline corticosterone, and blood glucose levels among restored grasslands planted with seed mixes of varying plant species diversity. In addition, we tested the ability of a conspecific song playback system to attract Henslow’s sparrows to previously unoccupied restored habitat. We selected 4 grassland planting types, cool-season, warm-season (newly planted and mature), and high diversity for our study to encompass the range of planting mixtures typically available to land managers. The most common bird species we encountered were Bobolink (Dolichonyx oryzivorus), Common Yellowthroat (Geothlypis trichas), Red-winged Blackbird (Agelaius phoeniceus), and Sedge Wren (Cistothorus platensis). Bird densities overall were not consistently higher or lower in any one of the 4 planting types. Bobolink densities, however, were higher in Cool-season fields than in any of the other field types. Models of the relationships between bird density/bird species richness and habitat characteristics revealed that both vegetation characteristics and food resources were important in explaining grassland bird densities. Our habitat models showed that different species, even those within a species category, were influenced by different habitat characteristics. Given the importance of cool-season, nonnative grass plantings for Bobolinks in our study, consideration must be given to the impact that elimination of these plantings may have on the future of Bobolink populations. Redwinged Blackbird nest survival was influenced by year, visual obstruction, and variation in