Tree stocking affects winter bird densities across a gradient of savanna, woodland, and forest in the Missouri Ozarks

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Savanna and woodland were historically prevalent in the midwestern United States, and managers throughout the area are currently attempting to restore these communities. Better knowledge of the responses of breeding and non-breeding birds to savanna and woodland restoration is needed to inform management.We surveyed abundance of winter resident birds across a gradient of tree stocking encompassed by savannas, woodlands, and non-managed forests in the Missouri Ozark Highlands, USA, and assessed the effect of stocking on bird densities. We conducted point counts at 560 locations along 42 transects on 10 sites across 2 winters between December and February, 2009-2011. We estimated detection probabilities and densities of birds using hierarchical, distance-based abundance models that incorporate covariates into estimation of both detection probabilities and densities.We fit models for 12 species with >49 detections and met model assumptions. Detection probabilities were affected by observer, temperature, wind speed, and stocking, and there was some level of support of the effects of stocking on the densities of all 12 species. Densities of black-capped plus Carolina chickadees (Poecile atricapillus, P. carolinensis), brown creeper (Certhia americana), golden-crowned kinglet (Regulus satrapa), and red-bellied woodpecker (Melanerpes carolinus) increased with stocking; whereas, densities of eastern bluebird (Sialia sialis), hairy woodpecker (Picoides villosus), and northern flicker (Colaptes auratus) were greatest at intermediate values of stocking. Although densities of 7 of the 12 species varied substantially across the range of stocking, all species used all 3 communities across a wide range of stocking. We provide winter densities of 12 of the most common overwintering bird species in the Missouri Ozarks; the relationships between their densities and stocking can be used to guidemanagement where managers have bird-species-specific objectives.