Woody plant and wintering grassland bird responses to summer prescribed burning in grazed and ungrazed Texas Mid-Coastal Prairies

Abstract

Concerned researchers have argued that winter region habitat losses may exacerbate observed declines of grassland birds on the breeding grounds. Yet few studies have investigated grassland bird habits during the non-breeding season. I examined how wintering habitat affinities and shifts in community organization among grassland birds are shaped by responses to summer fire and grazing management. Summer prescribed burns are thought to sustain remaining prairie parcels by deterring woody species succession and by restoring historical disturbance regimes presumed to favor tallgrass prairie plants. I identified woody community responses to summer prescribed burns. Summer fire had a greater impact on small shrubs than large shrubs or shrub cover. Data suggested that with appropriate rest periods, enough fine fuel can accumulate to sustain similarly hot summer burns among grazing contexts. I offer that a rest-rotational grazing regime provides managers operational flexibility to integrate prescribed burning and sustainable grazing pressures into their management plans. Despite often being grouped into a single guild, grassland species did not respond similarly to management disturbances. Species exhibited higher use according to specific ecological conditions within successional ecotypes. Data suggested that grassland birds responded to two patterns of prairie succession that occurred along different temporal landscapes. In the short term, grassland species responded to disturbance mediated herbaceous succession. But over the long term, if fire intervals lengthened and shrub communities progressed, then grassland bird habitat use declined in association with woody plant induced desuetude that threatens the traditional openness of tallgrass prairies. Indeed, the presence of several species, Le Conte's Sparrow, Sedge Wren, and Sprague's Pipit, rapidly declined in areas where shrub densities surpassed 100 ha-1 and shrub cover exceeded 30%. At Aransas National Wildlife Refuge, I examined wintering grassland bird habitat use separate from woody advancement in an ungrazed prairie ecosystem. Data demonstrated that following fire, species were preferentially occupying specific successional patches. I expect this general pattern was largely mediated by proximate responses to habitat structure as prairie plants recovered in subsequent growing seasons post-burn.