Breeding bird response to habitat and landscape factors across a gradient of savanna, woodland, and forest in the Missouri Ozarks

Abstract

Savanna and woodland were once common in the Midwest, but land use changes have led to increasing scarcity of these communities. These transitional habitats are being restored across the Midwest, but few studies have evaluated the response of wildlife to restoration or the vegetative gradient created by management. We conducted point counts for 25 songbirds at sites undergoing savanna or woodland restoration and nearby non-managed forest sites across the Ozark Highlands of Missouri during the 2009–2011 breeding seasons; these sites represented a gradient of canopy cover and tree density from savanna to woodland to forest. We estimated density of 17 species with ⩾50 detections using distance-based models, which adjust estimates by the detection probability. Bird densities were more strongly related to habitat structure, fire history, and landscape composition than simply whether a site was managed or non-managed. Mature forest species such as Acadian Flycatcher (Empidonax virescens), Northen Parula (Setophaga americana), Red-eyed Vireo (Vireo olivaceous), and Worm-eating Warbler (Helmitheros vermivorum) were generally more abundant at points with more trees, higher canopy cover, lower shrub density, and less frequent or no fire in the 20years prior to surveys. Woodland generalists such as Blue-gray Gnatcatcher (Polioptila caerulea), Eastern Wood-Pewee (Contopus virens), Great Crested Flycatcher (Myiarchus crinitus), Summer Tanager (Piranga rubra), and Yellow-billed Cuckoo (Coccyzus americanus) were generally more abundant at points with less landscape forest cover (10-km scale), more large and fewer small trees, intermediate to high canopy cover, lower shrub density, and recent or frequent fire. Early-successional species such as Eastern Towhee (Pipilo erythrophthalmus), Field Sparrow (Spizella pusilla), Indigo Bunting (Passerina cyanea), Kentucky Warbler (Geothlypis formosa), Prairie Warbler (Setophaga discolor), White-eyed Vireo (Vireo griseus) and Yellow-breasted Chat (Icteria virens) were generally more abundant at points with lower canopy cover, recent or frequent fire, and higher shrub density. Brown-headed Cowbirds (Molothrus ater) were more abundant at points with intermediate landscape forest cover and lower canopy cover. Restored sites provided breeding habitat for woodland generalists and early-successional species of conservation concern; however, managed landscapes with more open canopy and herbaceous ground cover may be required for species more indicative of open savannas.