Patch-burn grazing and demographic performance of grassland songbirds

Population declines in grassland birds are an emerging conservation crisis in North America.  Changes in rangeland management associated with intensification of agricultural production are thought to be negatively impacting birds in native grasslands.  We conducted a 2-year study at Konza Prairie LTER site to test the potential benefits of patch-burn grazing for grassland vertebrates.  Patch-burn grazing combines rotational fire with selective grazing by cattle to increase heterogeneity in vegetative structure.  We used transect surveys and nest searching to examine bird responses in five experimental treatments: season-long grazing with annual fire, patch-burn grazing with patches 0, 1, or 2 years post-fire, and an ungrazed site with annual fire.  Species richness of birds was highest in patch-burn pastures that had been rested from fire for 1-2 years.  Changes in bird abundance were species-specific: Brown-headed Cowbirds were common in all treatments, Dickcissels and Eastern Meadowlarks had reduced numbers in the year of burn in the patch-burn treatment, Grasshopper Sparrows and Upland Sandpipers preferred grazed sites, whereas Henslow's Sparrows were only found in unburned areas.  Estimates of demographic performance were based on 74 nests of four core species of grassland songbirds.  Dickcissels were a preferred host with high rates of nest parasitism by cowbirds (>90%) and averaged 2-4 cowbird eggs per host nest in all five treatments.  Nest survival was low across all treatments (7-20%), but unexpectedly, nest survival was highest in the patch-burn treatment in the year of burn, possibly because of density-dependent foraging strategies by predators.  Overall, our preliminary results indicate the greatest response to patch-burn grazing will be effects on bird densities and not demographic performance.  Patch-burn grazing has great potential to increase biodiversity of grassland obligate species.  However, species responses are unlikely to be uniform, highlighting a need to maintain habitat heterogeneity on private lands managed for cattle production.