Characteristics of Golden-winged Warbler territories in plant communities associated with regenerating forest and abandoned agricultural fields

Abstract

In the Appalachian portion of their breeding range, Golden‐winged Warblers (Vermivora chrysoptera) nest in shrubland and regenerating forest communities created and maintained by disturbance. Because populations of Golden‐winged Warblers have exhibited precipitous declines in population throughout their Appalachian breeding range, management activities that create or maintain early successional habitat are a priority for many natural resource agencies and their conservation partners. Within these early successional habitats, however, additional information is still needed concerning the relative importance of different vegetation features in selection of breeding territories by Golden‐winged Warblers. Our objective, therefore, was to use logistic regression to estimate the probability of territory‐level occupancy by Golden‐winged Warblers in north‐central Pennsylvania at two sites, each with its own early successional community, based on vegetation characteristics. Our communities were composed of shrublands and regenerating forest sites resulting from two disturbances: agriculture and forest fire. Despite differences in vegetation structure, portions of both study areas (regenerating forest and old field) supported territorial Golden‐winged Warblers. Probability of territory occupancy by Golden‐winged Warblers increased with percent blackberry (Rubus) cover in the regenerating forest community, and decreased as basal area and distance to microedge increased (i.e., as vegetation patchiness decreased) in both communities. These habitat features have also been found to influence other aspects of Golden‐winged Warbler breeding ecology such as nest‐site selection, pairing success, and territory abundance. Vegetation features influencing Golden‐winged Warbler territory establishment can differ among shrubland and regenerating forest communities, and management decisions and outcomes may be affected by these differences. Our study provides a starting point for a more comprehensive hypothesis‐driven occupancy survey to investigate features of the territories of Golden‐winged Warblers across a broader geographic range and in different vegetation communities.

Using a natural reference system to evaluate songbird habitat restoration

“…For Golden-winged Warblers occurring within shrub wetlands, we found a strong negative relationship between warbler abundance and canopy cover. This finding is consistent with the findings of several past studies suggesting that the species requires habitat with fewer trees (Confer and Knapp 1981, Askins 1994, Hunter et al 2001, Leuenberger et al 2017). This is not to suggest that Golden-winged Warblers breeding in shrub wetlands do not use trees or high-canopy areas but rather establish defended territories in highest densities within shrub wetlands with fewer trees in their interiors; it seems likely that Goldenwinged Warblers nesting within shrub wetlands may forage in mature canopy trees around the peripheries of these habitats.…”

“…Woody stems 1-2 m tall within the wetlands we studied were typically large shrubs and moderate-sized saplings, a vegetation size class understood to be important by previous work (Roth and Lutz 2004). It seems likely that woody vegetation of this size class facilitates the co-occurrence of herbaceous and woody cover types, a combination of features known to be important for the species (Confer and Knapp 1981, Klaus and Buehler 2001, Leuenberger et al 2017). …”

Ecology and Management of Golden-Winged Warblers (Vermivora Chrysoptera) and Associated Avian Species in the Allegheny Mountains of West Virginia

“…Our results appear to contradict Leuenberger et al (2017), who found that Goldenwinged Warbler occupancy was negatively associated with distance to micro-edge, with the species occupying territories with distances to micro-edge <3 m. However, we identified two important distinctions between the two studies that arise from their definition of micro-edge. Leuenberger et al (2017) defined distance to micro-edge as "any noticeable change in vegetation structure, i.e., change in vegetation height or species composition, such as a transition from grass to shrubs." First, micro-edges may occur between any vegetation types or even within a single vegetation type, whereas our study focused solely on shrubs.…”

“…as shrubs for this study so that our results would be comparable to other studies that commonly separate Rubus spp. from other woody shrubs , Leuenberger et al 2017.…”

“…For example, a study of Golden-winged Warbler occupancy on abandoned and low-intensity farmland in western Virginia developed a "clumpiness" index to visually assess the spatial arrangement of shrub patches around point count locations, ranging from scattered to contiguous (Bulluck and Harding 2010). Similarly, multiple studies measured distance to a "micro-edge" based on an observer's visual interpretation of any apparent change in vegetation height or composition , Leuenberger et al 2017. In addition to observer bias, this latter approach is not guided by research on the species' use, preference, or selection of certain edge characteristics within the nesting territory.…”