Response of ferruginous hawks to temporary habitat alterations for energy development in southwestern Alberta

Abstract

Temperate grasslands are among the most altered biomes worldwide, largely through anthropogenic modification. The rapid construction of renewable energy projects is necessary to accommodate growing energy demands and, when existing projects are upgraded, alterations to associated infrastructure are necessary. The direct effects of these developments on wildlife are relatively well understood (e.g., mortality risk), but there is little understanding of indirect impacts on wildlife breeding near developments. We applied a Before-During-After Control-Impact (BDACI) design to determine the influence of high-voltage transmission line alterations on an Endangered population of Ferruginous Hawk (Buteo regalis), in southern Alberta, Canada. Using data collected between 2013-2019, we compared the response of breeding hawks to three phases of development between control and impact sites to determine if the number of transmission towers on the landscape could influence this local population and if alterations could result in a sink population or ecological trap. Generalized linear mixed models were used to test for five responses: (1) Ferruginous Hawk nest density, (2) nest success, (3) productivity, (4) nest site re-occupancy, and (5) changes to nesting raptor and raven community composition. We found no effect of phase and site on nest success, productivity, or re-occupancy. However, nest densities increased significantly by >37% after towers were added but returned to pre-construction levels after tower removal. Additionally, community composition changed significantly with higher variability near impact sites. Our study is the first to test for population-level effects of energy development on an At Risk raptor using a robust BDACI design. Our experimental design demonstrates that the availability of nesting structures limits the size of this population, providing evidence that this population can be increased by adding nesting substrates (e.g., trees or nest platforms) to the landscape.