Avian occupancy varies with habitat structure in oak savanna of the south-central United States

Abstract

Oak savanna, once widespread across central North America, has functionally vanished from most of its range because of land conversion or fire suppression, but much oak savanna remains in the Cross Timbers ecoregion of the south-central United States. We quantified avian habitat associations across a gradient from open oak savanna to woodland, to closed canopy forest in the Cross Timbers of southeastern Kansas. We surveyed breeding bird species in 2012 and 2013 and modeled species-specific occupancy in relation to habitat variables. Several species, including the northern bobwhite (Colinus virginianus), yellow- billed cuckoo (Coccyzus americanus), downy woodpecker (Picoides pubescens), Bewick's wren (Thryomanes bewickii), northern mockingbird (Mimus polyglottos), field sparrow (Spizella pusilla), dickcissel (Spiza americana), and orchard oriole (Icterus spurius) were associated with lower levels of tree density or canopy cover (i.e., savanna-woodland). Species associated with greater levels of tree density or canopy cover at some spatial scale included eastern wood-pewee (Contopus virens), white-breasted nuthatch (Sitta carolinensis), blue-gray gnatcatcher (Polioptila caerulea), and indigo bunting (Passerina cyanea). Occupancy of eastern wood-pewee and blue grosbeak (Passerina caerulea) were highest at intermediate levels of canopy cover (50- m radius) and tree density, respectively. Occupancies of eastern wood-pewee, northern mockingbird, lark sparrow (Chondestes grammacus), indigo bunting, and brown-headed cowbird (Molothrus ater )w ere variously related to shrub density, which was unrelated to tree cover or density across the savanna-forest gradient. We expect the savanna-associated species would benefit from reduction in tree density to savanna-like habitat (tree canopy cover � 25%) within forests that were formerly savanna. 2015 The Wildlife Society.