Wintering grassland bird responses to vegetation structure, exotic invasive plant composition, and disturbance regime in coastal prairies of Texas

Many migratory grassland passerines complete their annual life cycle within the United States and investigations into wintering ecology of these species are scarce, particularly in ecoregions where habitat quality is considered to be compromised, such as the coastal prairie of Texas. During 2008-2010, we investigated wintering grassland bird ecology as related to coastal prairie composition and management practices on the mid-upper Texas coast. To quantify grassland bird composition and density among management regimes, we performed 260 transect surveys on 40 different study site pastures deployed among 7 different management regimes, varying in plant community composition as well as frequency (or occurrence) of burning, grazing, and mowing from 29 October 2008-7 April 2009 and 17 November 2009-17 March 2010. A total of 79 bird species (48 species in 2008-2009 and 66 species in 2009-2010) were recorded during this study. Sites that were recently (<2 years prior) grazed, burned, or mowed tended to have the greatest species richness of obligate grassland bird species. Management regime and the resulting habitat characteristics also appeared to influence densities of Le Conte's Sparrow (Ammodramus leconteii), Sedge Wren (Cistothorus platensis), and Sprague's Pipit (Anthus spragueii), with the former two species selecting areas that had not been recently burned, grazed, or mowed and were characterized by greater vertical vegetation density and litter depth, respectively. Conversely, Sprague's Pipit selected recently burned, grazed, or mowed prairies, characterized by less litter depth and percentage of shrubs nearby. More cosmopolitan species, such as Eastern Meadowlark (Sturnella magna) and Savannah Sparrow (Passerculus sandwichensis) occurred equally among management regimes. Despite similar species richness in floristically disturbed sites, nonnative vegetation appeared to negatively influence species with specific habitat requirements such as Sprague's Pipit, Sedge Wren, and Le Conte's Sparrow. In order to increase wintering avian diversity, coastal prairie habitat conservation and management in Texas should focus on restoring management regimes (i.e., burning, mowing, and grazing) that create heterogeneous environments, while maintaining native vegetation communities.