Avian Conservation and Ecology (Jun 2023)
Evaluating the effects of Natural Resources Conservation Service project implementation on the disturbance-dependent avian community with implications for Blue-winged Warblers
Abstract
The Blue-winged Warbler (Vermivora cyanoptera) is a songbird that breeds in eastern deciduous forests of North America. The species is declining, partially due to declines in forest disturbances. According to the umbrella species concept, management actions implemented to benefit other critically declining disturbance-dependent species like the Cerulean (Setophaga cerulea) and Golden-winged (Vermivora chrysoptera) warblers should positively affect Blue-winged Warbler site occupancy and species richness of shrubland and grassland birds. Similarly, determining if the umbrella concept is supported by relating species richness of disturbance-dependent avian guilds would support continued funding for species-specific conservation and management. Our goal was to evaluate if Natural Resources Conservation Service (NRCS) projects in West Virginia implemented for Cerulean and Golden-winged warblers also positively affected Blue-winged Warbler site occupancy and the disturbance-dependent avian community. We hypothesized that Blue-winged Warbler single-season occupancy and species richness for shrubland and grassland bird species would be greater on treated sites than on untreated sites. We also included other vegetation variables (i.e., percent cover of grasses, forbs, etc.) and spatial variables (i.e., elevation (m), ecoregion, etc.) that could affect Blue-winged Warbler site occupancy. We conducted point count surveys at 341 total locations distributed among 20 private properties managed for Golden-winged Warblers (n = 147); 19 private properties managed for Cerulean Warblers (n = 197); and two properties managed for both species during 2019–2020. Treatments included a variety of management practices (i.e., brush management) following specific guidelines to improve Cerulean and Golden-winged warbler habitat. We identified and defined untreated sites as either pre-treatment sites with planned management that had not yet occurred, or as reference sites, which were outside of treatment areas and representative of pre-treatment vegetation structure conditions. Contrary to our hypotheses, treated points had lower Blue-winged Warbler site occupancy than untreated points by 34–44% depending on ecoregion (Central Appalachians, Ridge and Valley, Western Allegheny Plateau), and shrubland and grassland avian guild richness were not different at untreated and treated locations. Thus, NRCS conservation project implementation for Cerulean and Golden-winged warblers did not meaningfully affect Blue-winged Warbler site occupancy or associated shrubland and grassland bird avian richness. We detected Blue-winged Warblers across the range of elevations surveyed (244–917 m), suggesting that their breeding distribution is continuing to expand into higher elevations in the Central Appalachians. Additionally, Blue-winged Warbler site occupancy was positively correlated with shrubland conditions within 100 m of survey points and decreased with increasing basal area within 100 m of survey points. Thus, management that increases the amount of shrubland in the Central Appalachians has potential as a conservation action to benefit Blue-winged Warbler site occupancy.
