No abstract

Recent trends in renewable energy development in the United States (U.S.) show that new installed capacity of utility-scale solar energy has exceeded 30% of total installed capacity of all sources per year since 2013. Photovoltaic solar energy provides benefits in that no emissions are produced; however, there are potential impacts from photovoltaic solar development on birds that include habitat loss and potential for collision mortality. Only 2 papers in the peer-reviewed literature present fatality information from fatality monitoring studies at a photovoltaic utility-scale solar energy facility; however, more data exists in unpublished reports. To provide a more comprehensive overview of bird mortality patterns, we synthesized results from fatality monitoring studies at 10 photovoltaic solar facilities across 13 siteyears in California and Nevada. We found variability in the distribution of avian orders and species among and within Bird Conservation Regions, and found that water-obligate birds, which rely on water for takeoff and landing, occurred at 90% (9/10) of site-years in the Sonoran and Mojave Deserts Bird Conservation Region. We found that a cause of mortality could not be determined for approximately 61% of intact carcasses, and that approximately 54% of all carcasses were feather spots, introducing uncertainty into the interpretation of the fatality estimates. The average annual fatality estimate we calculated for photovoltaic solar (high-end estimate of 2.49 birds per megawatt per year) is lower than that reported by another study (9.9 birds per megawatt per year) that included one photovoltaic facility. Our results provide a summary of fatalities in bird conservation regions where the facilities are located, but expanding our conclusions to new regions is limited by the location of facilities with fatality monitoring data.

No abstract

As technology and energy development increase, undeveloped land and land traditionally used for agriculture now host structures not part of the historical landscape. These structures (e.g., communication towers, transmission lines) are taller than many objects in natural landscapes. Concerns have been raised regarding the effects of tall structures on birds, primarily functional habitat loss due to avoidance. Two hypotheses have been advanced to explain observed patterns of birds near tall structures: increased perceived predation risk and neophobia. We examined the literature and used a vote-counting methodology to document 1) the reported direction (positive or negative) of a potential tall-structure effect, 2) whether the effect of tall structures can be isolated from other effects of development, 3) whether the study design lent itself to drawing a supportable conclusion, and 4) whether the authors suggested a causal mechanism for any observed pattern. We did not detect any consistent response to tall structures, nor did we find evidence to support the two hypotheses. In addition, a structure's "tallness" could not be isolated from other factors associated with development such as human activity. Understanding causal mechanisms is important for management and conservation because observed effects might not be related to the tallness of the structure but to other factors that could be managed, such as timing of construction. Our results suggest that the effect of tall structures on birds is not well understood, and focused studies that examine before-andafter effects and specific causal mechanisms are needed to support effective project siting and conservation planning. Ó