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

Abstract

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%).