Topographic Patterns of Nest Placement and Habitat Quality for Grassland Birds in Tallgrass Prairie

Abstract

Much of the tallgrass prairie remaining in North America occurs in hilly regions, such as the Flint Hills of Kansas and Oklahoma. Despite the conservation importance of these areas for grassland birds, little is known about how topographic variation in habitat affects the nesting ecology of these species. We examined topographic patterns of nest distribution, daily nest survival and nest-site selection for three species: Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum) and Eastern Meadowlark (Sturnella magna). Dickcissels shifted from nesting more in lowlands to uplands as the season progressed. Grasshopper Sparrows and Eastern Meadowlarks generally nested in midland habitats, but seasonal differences were still evident in the relative proportions of nests found in lowlands vs. uplands. Topography did not affect nest survival of Dickcissels or Grasshopper Sparrows and had only a marginal effect on nest survival for Eastern Meadowlarks. Nest survival for Dickcissels and Grasshopper Sparrows was highly dependent on nest-site vegetation, however. Dickcissels and Eastern Meadowlarks both experienced greater daily nest survival with increasing vertical vegetation structure at nest sites, whereas daily nest survival for Grasshopper Sparrows increased with increasing cover of litter and grass. Although topography may not affect nest survival directly, it may have indirect effects mediated through nest-site vegetation because of selective nest placement. For example, Dickcissels and Eastern Meadowlarks selected sites with greater vertical vegetation structure than generally available, even in upland sites where vegetation structure was reduced. Conservation planning for grassland birds may thus need to consider how topographic variation affects habitat quality within hilly regions where much of the remaining tallgrass prairie occurs.