Breeding season space use and habitat selection by Blue-winged Warblers in managed shrublands

The Blue-winged Warbler (Vermivora cyanoptera) is a relatively understudied shrubland-associated species that has experienced sustained population declines in portions of its breeding range. Detailed evaluations of Blue-winged Warbler breeding season habitat requirements are needed to inform ongoing and future conservation efforts and, ultimately, stem population declines. Here, we use radio telemetry, field-measured vegetation data, and Light Detection and Ranging (LiDAR) to assess Blue-winged Warbler breeding season space use and habitat selection in southwest Pennsylvania. During the 2019 and 2020 breeding seasons, we tracked 27 male Blue-winged Warblers and mapped their core home ranges (50% kernel density estimate) and total home ranges (95% kernel density estimate). The scale of Blue-winged Warbler space use was similar to that of other Vermivora with a mean total home range size of 12.9 ha and a mean core home range (i.e., high use area of the home range) size of 2.9 ha. Blue-winged Warbler core home ranges had more shrub cover and herbaceous cover but less overhead cover and leaf litter than peripheral (area of total home range outside of core area) home ranges. Core areas were also dominated by shrubland and forest-shrubland ecotone, while peripheral home ranges contained greater forest cover. Finally, LiDAR data suggested that core home ranges contained more structural heterogeneity (rugosity metrics) and more short-stature vegetation (% returns between 1 and 5 m) than peripheral home ranges. These results suggest that although Blue-winged Warblers require shrubland communities in the core of their breeding season home ranges, the availability of adjacent forest cover that forms structurally complex ecotones is also essential. Therefore, conservation practices that aim to create or maintain habitat for this declining bird should promote structurally complex shrubland adjacent to forest-shrubland ecotones.