Grassland bird associations in a managed agricultural matrix
Continued declines of grassland bird populations in the U.S. are largely attributed to grassland loss from conversion to agriculture. Habitat establishment efforts by the U.S. Department of Agriculture (USDA) may stem these declines given adequate ecological insight to guide management protocols. My research evaluated bird responses to four USDA conservation practices in the Mississippi Alluvial Valley, Mississippi, including (1) early-succession afforestation blocks, (2) early-succession, 60-m wide riparian forest buffers, (3) diverse-planted, 30-m wide filter strips, and (4) monotypic-planted, 30-m wide filter strips. I collected data from May to August, 2005-2007, to investigate the influence of conservation practice design, landscape context, and microhabitat on avian community structure, grassland bird nest ecology, Dickcissel fledgling ecology, and Northern Bobwhite landscape-level associations. Strip-transect surveys showed that Red-winged Blackbird (43%) and Dickcissel (42%) dominated bird communities, but other abundant species included Eastern Meadowlark, Indigo Bunting, Mourning Dove, and Northern Bobwhite. Bird diversity was greater in blocks than buffers, and diverse filter strips had the greatest bird densities. I found and monitored large samples of Dickcissel (n = 733) and Red-winged Blackbird (n = 409) nests in all practices, with large blocks attracting the greatest nest densities. Dickcissel nest success (22.9%) positively correlated with nest height, but negatively correlated with nearby (30 m) rowcrop area, grass cover, and horizontal vegetation cover. Red-winged Blackbird nest success was highest in diverse filter strips (23.4%) than on average (8.6%) and positively correlated with nest height, but negatively correlated with litter cover. I attached radio transmitters to 416 Dickcissel nestlings to track fledgling survival. Red imported fire ants and snakes were the predominant predators of fledglings and caused ≥65% of all mortality, which was greatest (83%) ≤2 days postfledging. Fledgling survival positively correlated with age, mass, and perch height, but negatively correlated with time in season, grassland area and edge density in the landscape. I counted 302 Northern Bobwhites at 100 locations in a 7,818 ha region and found 3.3 times more birds in a managed than unmanaged habitats. Their abundances were negatively associated with rowcrop area, wooded area, developed area, and landscape contagion, but positively influenced by all conservation practices, especially diverse filter strips. I recommend integrating 30-m wide conservation buffers within a block-based conservation management system to maximize grassland bird benefits. I also suggest that buffers be managed to maximize vegetative structural complexity in concert with moderate cover.