Winter bird habitat use at multiple scales in a heterogeneous tallgrass prairie

In the U.S. Great Plains, the reduction in grassland heterogeneity due to traditional management practices, that typically include large-scale annual burns and uniform grazing, has been shown to reduce breeding bird diversity. The effect of that loss of heterogeneity on wintering grassland birds, including multiple species of conservation priority, has not been evaluated. The interaction of fire and grazing historically played a major role in shaping North American grasslands to be both spatially and temporally heterogeneous, and wintering grassland birds that evolved under such conditions may have habitat requirements that homogeneous structure may not provide. To investigate this relationship, I studied the habitat use of wintering grassland birds in a landscape managed to promote heterogeneity through the interaction of fire and grazing. I used an area-search method to survey 148 1-ha plots for birds during the winters of 2009 and 2010 in patch-burned and season-long stocking pastures at The Nature Conservancy's Tallgrass Prairie Preserve in Osage Co., Oklahoma, USA. I characterized habitat use at multiple scales for four species, and evaluated their response using information-theoretic methods. The abundance of some species was related to specific attributes of patches and broad-scale features such as the distance to utility poles, rather than heterogeneity. At fine-scales, however, model selection revealed that Le Conte's Sparrows (Ammodramus leconteii) and Sedge Wrens (Cistothorus platensis) were associated with increasing vegetation height, while Smith's Longspur (Calcarius pictus) occurred at sites with low litter depth and shorter structure. Management that promotes heterogeneity may provide habitat for species that specialize in habitat at opposite ends of the vegetation structure gradient.