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

Abstract

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 v the availability of invertebrate food resources throughout the nesting season. We found evidence for a difference in daily nest survival among planting types (P=0.06). Specifically, estimated nest survival was more than twice as high in mature warm-season fields (36%) than in cool-season fields (14%). Red-winged Blackbird nestling size at fledging differed among grassland planting type. Male nestlings were larger than females at fledging with regard to mass, wing, and tarsus measurements. Nestling growth rates did not differ either among grassland restoration planting types or between sexes. Invertebrate food resource availability did not appear to affect growth rates of nestling Red-winged Blackbirds. Redwinged Blackbird nestling baseline corticosterone levels were lower in the warm-season planting type than in either cool-season or high diversity plantings. We found no evidence of differences in baseline corticosterone levels or blood glucose levels between males and females. We found no relationship between baseline corticosterone levels and body mass or between base...

Adaptive management in native grasslands managed by the U.S. Fish and Wildlife Service—Implications for grassland birds

“…In this study, sedge wrens were more abundant in tallgrass and mixed-grass prairie units that were rested for more than five growing seasons than in managed NPAM units. Similar to this study, high vertical heightdensity or vertical obstruction was identified as an important habitat feature for sedge wrens by Sample (1989), Delisle andSavidge (1997), andVogel (2011). Sedge wren preference for grasslands with greater litter depth also was noted by Delisle and Savidge (1997), Bakker and others (2002), Renfrew and Ribic (2002), Pillsbury (2010), and Vogel (2011).…”

The effects of management practices on grassland birds—Sedge Wren (<i>Cistothorus stellaris</i>)

“…In eastern Nebraska and western Iowa, Sedge Wren density was lowest in warm-season grasslands planted with a high-diversity seeding mixture and highest in warm-season grasslands planted with a low-diversity seeding mixture (Cox and others, 2014). In Iowa, Sedge Wren density was higher in grasslands planted to cool-season, tame grass species than in newly planted grasslands seeded to warm-season, native grass species (Vogel, 2011). Sedge Wren density did not differ, however, among several other plantings, including mature stands of native, warm-season grasslands and grasslands planted to a high-diversity mix of over 40 species of native grasses and forbs (Vogel, 2011).…”

“…In Iowa, Sedge Wren density was higher in grasslands planted to cool-season, tame grass species than in newly planted grasslands seeded to warm-season, native grass species (Vogel, 2011). Sedge Wren density did not differ, however, among several other plantings, including mature stands of native, warm-season grasslands and grasslands planted to a high-diversity mix of over 40 species of native grasses and forbs (Vogel, 2011). Within CRP filter strips in Iowa, Sedge Wren density did not differ between strips planted to cool-season plant mixtures and strips planted to warm-season mixtures (Henningsen and Best, 2005).…”

“…Suitable Habitat 3 Pillsbury and others, 2011;Bruinsma, 2012;Igl and Johnson, 2016;Elliott and Johnson, 2017). The species inhabits planted cover (for example, Conservation Reserve Program [CRP] fields and dense nesting cover [DNC]) (Renken and Dinsmore, 1987;Johnson and Schwartz, 1993b;Dhol and others, 1994;Hartley, 1994;Jones, 1994;King and Savidge, 1995;Best and others, 1997;Prescott and Murphy, 1999;McCoy and others, 2001;Roth and others, 2005;Vogel, 2011;Osborne and Sparling, 2013), riparian filter strips (Henningsen and Best, 2005), grassed waterways (Bryan and Best, 1994), and grassy terraces (Hultquist and Best, 2001). Sedge Wrens occupy many types of mesic grasslands and wetlands.…”

“…In Iowa tallgrass prairies and grasslands restored to tallgrass species, Sedge Wren densities were positively correlated with the percentage of total vegetation cover (Fletcher and Koford, 2002). In Iowa restored grasslands, Sedge Wren densities were positively associated with vegetation height-density and litter depth (Vogel, 2011). In Wisconsin, Sedge Wrens nested in CRP fields planted to switchgrass, which provided tall, dense vegetation (Roth and others, 2005).…”