The invasive red imported fire ant (Solenopsis invicta) has negatively affected a host of taxonomic groups throughout its acquired North American range. Many studies have hypothesized indirect trophic impacts, but few documented those impacts. We evaluated invertebrate abundance as a factor limiting juvenile survival of the endangered Attwater's prairie‐chicken (Tympanuchus cupido attwateri), and whether fire ants reduce invertebrate numbers and biomass. From 2009–2013, we monitored survival of Attwater's prairie‐chicken broods (n = 63) with radio telemetry during the first 2 weeks post‐hatch and collected daily invertebrate samples at brood sites. Broods located in areas with the highest median invertebrate count (338 invertebrates/25 sweeps) had a survival probability of 0.83 at 2 weeks post‐hatch compared to 0.07 for broods located in areas with the lowest median invertebrate count (18 invertebrates/25 sweeps). During 2011–2012, we evaluated the reduction of fire ants on invertebrate numbers and biomass by aerially treating areas with Extinguish Plus™ in an impact‐reference study design. Treated fields had 27% more individual invertebrates and 26% higher invertebrate biomass than reference fields. Our results clearly document that invertebrate abundance affects Attwater's prairie‐chicken brood survival and that fire ants may indirectly contribute to low brood survival by suppressing invertebrate abundance. We posit that within the fire ant's acquired North American range, fire ants are likely contributing to declines of other insectivorous species. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

DISCLAIMERRecovery plans delineate reasonable actions believed necessary to recover and/or protect listed species. Plans are published by the U.S. Fish and Wildlife Service (USFWS), sometimes prepared with the assistance of recovery teams, contractors, State agencies, and others.

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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.

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