Grassland bird responses to a fire-grazing interaction in a fragmented landscape

Grassland birds have experienced widespread population declines throughout the North American tallgrass prairie region, largely as a result of habitat loss and the homogenization of remaining fragments. Recent work in relatively extensive grasslands has demonstrated that mimicking historic disturbance patterns using a fire-grazing interaction can increase the abundance and diversity of grassland birds by providing more habitat heterogeneity. We examined the efficacy of management that restores a fire-grazing interaction for promoting avian diversity in a fragmented landscape. We examined community and population responses of obligate and facultative grassland bird species at 13 experimental research pastures in the Grand River Grasslands of Iowa and Missouri (USA), divided among three treatments: (1) spatially discrete fires and free access by cattle ("patch-burn grazing"), (2) free access by cattle and a single complete burn ("grazed-and-burned"), and (3) a single complete burn with no cattle ("burned-only"). We expected that patch-burn grazing would produce a bird community intermediate between those of the grazed-and-burned and burned-only treatments, because it would provide habitat for species associated with both. However, community structure on pastures managed using patch-burn grazing instead diverged significantly from both of the other treatments, though most individual species showed few population responses to treatment. Differences in community structure were most highly correlated with visual obstruction and wooded edge density in the landscape, suggesting bird communities are differentiated not only by their structural habitat requirements, but also by the varying degrees of sensitivity to landscape fragmentation of their component species.