Factors Affecting Survival of Attwater’s Prairie-Chicken Broods

Abstract

Annual population changes of most grouse, including the imperiled Attwater’s prairie-chicken Tympanuchus cupido attwateri , are driven by annual reproductive success.  Previous research identified poor survival of chicks as a primary bottleneck for recovery of this species.  We evaluated the relative importance of 26 factors in 5 categories (weather and topography, habitat, plant phenology, time and site, hen characteristics) on Attwater’s prairie-chicken brood survival to 2 weeks post-hatch (the period when chick mortality is highest) and on the number of chicks per brood at 6 weeks post-hatch (when chicks are capable of independent survival).  Factors with most support for predicting brood survival to 2 weeks included invertebrate dry mass, ordinal date, an index to maximum photosynthetic activity of vegetation from multispectral imagery, and proportion of brood locations within areas treated to suppress red imported fire ants Solenopsis invicta .  Broods were most likely to survive if they hatched between early and late May and were located within areas (1) that were treated to suppress red imported fire ants, (2) where vegetation produced intermediate values for the maximum photosynthetic activity index, and (3) that supported high invertebrate biomass.  The number of chicks per brood surviving to 6 weeks post-hatch was best predicted by a nonlinear relationship with a drought index during the first 2 weeks post-hatch, and was maximized when average values of the drought index indicated moderately depleted soil moisture, but not severe drought.  Our finding that the average drought index during the first 2 weeks after hatch had more support for predicting the number of chicks per brood at 6 weeks than the average drought index for the entire 6 weeks emphasizes the importance of the first 2 weeks for Attwater’s prairie-chickens.  This comprehensive analysis of factors affecting Attwater’s prairie-chicken brood survival provides valuable information to guide management and recovery efforts for this species.