Non-Native Grasses Reduce Scaled Quail Habitat

Non-native grasses are frequently sown in the southwestern United States for livestock forage and erosion control. These grasses often spread from areas where they are planted and replace native grasses and forbs. We tested the hypothesis that chestnut-bellied scaled quail (Callipepla squamata castanogastris) avoid locations dominated by non-native grasses. We trapped scaled quail at 5 different sites in southern Texas, USA, and located quail fitted with necklace-style transmitters 3 times/week during 2013–2014. We manually delineated plant communities using aerial maps and on-the-ground knowledge of the study sites. We examined second-order (home-range scale) selection by comparing proportion of the areas of plant communities within 62 scaled quail home ranges (used) paired with random home ranges (available). We examined third-order (within-home-range scale) selection by comparing the composition of bird location (used) and random (available) points based on proportion of points within plant communities. For both home-range scale and within-home-range scale analyses, we used non-parametric multivariate analysis of variance with 9,999 random permutations. We examined fourth-order (organism-centered) selection by measuring vegetation variables at used and available locations and then estimating the relative probability of use of vegetation variables and by estimating continuous selection functions for variables that were influential in determining relative probability of use. Buffelgrass (Pennisetum ciliare) and Old World bluestems (Bothriochloa spp., Dichanthium annulatum and other Dichanthium spp.) comprised 99% (95% CI = 98–100%, n = 143 sites where non-native plants occurred) of the non-native grasses in our study areas. Scaled quail avoided non-native and riparian plant communities at the home-range and within-home-range scales of selection. At the organism-centered scale of selection, odds of use by scaled quail decreased 28% for every 10% increase in non-native grass cover and increased 12% for every 10% increase in shrub canopy cover. Scaled quail avoided locations with >10% canopy cover of non-native grasses. Based on avoidance at 3 scales of selection, dominance of buffelgrass and Old World bluestems degrades habitat for scaled quail. Spread and sowing of non-native grasses and brush clearing may be partly responsible for declines in scaled quail populations.