Survival of grasshopper sparrows (Ammodramus savannarum) during two important life stages in grassland managed with fire and grazing

Abstract

Patch-burn grazing is a management framework that promotes heterogeneity in grasslands, similar to the structure grasslands birds evolved inhabiting. Published studies on patch-burn grazing have been conducted on large, contiguous grasslands and only one of these studies has investigated the reproductive success of grassland birds. We assessed the effects of patch-burn grazing (grazing, one third of the pasture burned annually) compared with a more traditional graze-and-burn treatment (grazing, entire pasture burned every third year) on nests of grasshopper sparrows (Ammodramus savannarum) in fragmented grasslands. We modeled grasshopper sparrow nest survival as a function of multiple biological and ecological factors. Constant daily survival rates were greater in patch-burn grazing pastures than in graze-and-burn pastures (patch-burn grazing rate = 0.930, burnand-graze rate = 0.907). Multiple factors were significant in survival models including year, stage of nest, a negative effect of nest age, and a negative effect of cool-season grass abundance within five meters of the nest. Our findings represent grassland bird survival in small-scale, fragmented grassland similar to many found throughout the corn-belt region of the United States. Results showed that survival rates were the highest in pastures managed with patch-burn grazing, but multiple factors influenced grasshopper sparrow survival. Results emphasize the importance of researchers using multiple covariates when examining