Long-Term Changes in Nesting Raptor Communities after Construction of Wind Power Projects

Abstract

We evaluated changes in communities of nesting raptors and Common Ravens (Corvus corax) in the upper Columbia Basin of the Pacific Northwest, USA, at wind power projects 1–18 yr post-construction. Relative abundance of nests for anthropogenically sensitive species, including Golden Eagles (Aquila chrysaetos), Ferruginous Hawks (Buteo regalis), and Prairie Falcons (Falco mexicanus), declined on project sites (n = 18), whereas Common Ravens increased on project sites and reference sites (n = 4). We used a Bayesian approach to understand community shifts as driving declines and to determine the effect of wind power vs. other factors on species composition. Golden Eagles, Ferruginous Hawks, and Prairie Falcons each experienced twofold decreases in their proportions in the raptor communities on wind project sites compared to reference sites. Declines on reference sites were consistent with decreasing populations of these species on the larger landscape due to multiple environmental factors. Case histories of territory occupancy for Ferruginous Hawks and Golden Eagles documented over multiple years during the study showed that adult turbine-strike mortality and repeated mortality of replacement adults created localized population sinks. We believe compositional shifts in the nesting guild were also facilitated by increases in competing and/or predatory species more adapted to nesting in altered habitats, principally Common Ravens and Great Horned Owls (Bubo virginianus). Commitment to long-term monitoring and establishment of control sites would improve our understanding of the contribution of wind power development to population declines for nesting species that are less tolerant of anthropogenic activities and habitat alterations across landscapes.