Using a natural reference system to evaluate songbird habitat restoration

摘要

The Golden-winged Warbler (Vermivora chrysoptera) is an imperiled songbird that breeds in early-successional plant communities of eastern North America. Conservation efforts on the breeding grounds have become a priority because population declines are thought to be driven, in part, by the loss of breeding habitat. Although the species is known to use a variety of upland and wetland cover types, the majority of previous research on the species has been conducted in uplands. Although patterns of Golden-winged Warbler habitat use within anthropogenic upland communities are well understood, such information within naturally occurring habitats are scant. We compared Golden-winged Warbler densities in natural shrub-wetlands and nearby upland timber harvest that conformed to species-specific habitat guidelines of the Poconos Region of Pennsylvania. We also identified vegetation characteristics of natural shrub-wetlands associated with high warbler abundance. Our analyses suggest that timber harvests and natural shrub-wetlands of the Poconos supported similar densities of Golden-winged Warblers. N-mixture models suggested that natural shrub-wetlands with low canopy cover and high densities of 1-2 m tall woody stems hosted more Golden-winged Warblers. Wetland complexes comprising more edge and those with more emergent wetland types supported the highest warbler abundances. This suggests that the species requires edges when it occurs within shrub-wetlands, a pattern not observed within our timber harvests, which were designed to have adequate tree cover throughout. Findings from our study combined with those from concurrent research evaluating Golden-winged Warbler reproductive success suggests that timber harvests following Golden-winged Warbler habitat guidelines have similar capacity as natural shrub-wetlands to support breeding populations. A future effort to quantify the potential of different wetland types to host breeding Golden-winged Warblers is warranted. Such information used in combination with timber harvest planning will provide insight for landscape-level conservation that considers maintaining appropriate amounts of nesting habitat to sustain Golden-winged Warblers in this region.