Disturbance, but not the right kind: Exurban development does not create habitat for shrubland birds

Exurban development (i.e., low-density residential housing) comprises at least 25% of the contiguous United States and disturbs the natural landscape, typically impairing habitat for forest interior songbirds and creating habitat for urban-adapted species. However, it is poorly known how exurban development affects shrubland birds, which require disturbance to create habitat (i.e., early successional vegetation). Therefore, our objective was to explore landscape patterns associated with shrubland bird occupancy in a forested region undergoing extensive exurban development. To address this objective, we conducted point counts across a natural-exurban gradient in Macon County, North Carolina, USA, and measured 8 land-cover covariates within 200 m and 1,000 m of survey sites. The covariates were percent canopy cover (CANOPY), contagion (CONTAG), percent of the landscape (PLAND) that was developed (DEV), elevation (ELEV), PLAND forest (FOREST), forest edge density (ED DF), Simpson's landscape diversity index (SIDI), and PLAND shrub (SHRUB). We modeled occupancy for 12 shrubland species using a hierarchical occupancy model that accounts for false positive detections. We fit a global model that incorporated all non-collinear covariates and used stochastic search variable selection to determine which covariates showed a relationship with occupancy. The most frequently selected covariate was CANOPY (8 species), followed by ELEV (5 species), DEV (4 species), SIDI (3 species), and CONTAG (2 species). CANOPY and DEV were negatively associated with occupancy. SIDI and CONTAG are both metrics of landscape heterogeneity; heterogeneity was positively associated with occupancy. Additionally, of the study species, generalists showed the highest occupancy rates, while specialists showed the lowest occupancy rates. We suggest that the associations between occupancy and canopy cover and landscape heterogeneity are logical because natural disturbance, in addition to creating early successional habitat, decreases canopy cover and increases landscape heterogeneity. Furthermore, we suggest that exurban development can drive these patterns. but, given the negative (or neutral) relationship between DEV and shrubland bird occupancy, we hypothesize that exurban development as a form of disturbance does not generate early successional habitat. We conclude that exurban development will benefit only a small subset of urban-adapted shrubland species without creating habitat for most shrubland birds, despite exerting considerable disturbance to forested landscapes.