Effects of conservation practices on bird nest density and survival in intensive agriculture

Nest density and survival of two farmland birds (dickcissel, Spiza americana and red-winged blackbird, Agelaius phoeniceus) were evaluated in four early-succession conservation practices: (1) large forest block [6–8 year old trees], (2) riparian forest buffer [1–3 year old trees], (3) monotypic switchgrass [Panicum virgatum] buffer [no trees], and (4) diverse forb-native grass buffer [no trees] over three years (2005–2007). We modeled daily survival of dickcissel (n = 733) and red-winged blackbird (n = 414) nests as a function of nest-site, patch, and landscape covariates. Dickcissels nested in greater densities (3.5 times) in large blocks than any buffers, and of non-wooded buffers, they preferred those with diverse vegetation. Dickcissels largely nested in buffers only early in the season. Dickcissel nest success was 22.9% on average and was similar among conservation practices except riparian forest buffers, in which they apparently suffered from high densities of red imported fire ants (Solenopsis invicta) and low vegetative cover. Dickcissel nest success related positively to nest height, but negatively to grass cover, horizontal vegetation density, and proximity (<30 m) to row-crop fields. Red-winged blackbirds had low overall nest success (8.6%) across conservation practices, though substantially higher for nests in diverse forb-native grass buffers (23.4%).