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Quantifying the rate of turbine collision mortality for raptors has been the primary focus of research at wind energy projects in Europe and the United States. Breeding adults and fledglings may be especially prone to collisions, but few studies have assessed the consequences of increased mortality and indirect effects from this type of development activity on reproduction. We examined the influence of wind turbines and other factors on nest success and survival of radio-marked juveniles during the post-fledging period for 3 sympatric breeding Buteo species in the Columbia Plateau Ecoregion (CPE), Oregon, USA. Nest success for ferruginous hawks (Buteo regalis) decreased as the number of wind turbines within the home range buffer (32 km2) increased. There was no effect of turbines on nest success for red-tailed hawks (Buteo jamaicensis) or Swainson's hawks (Buteo swainsoni). Of 60 nestlings radio-marked from all 3 species, we found no evidence that any were killed as a result of collisions with wind turbines after fledging. This was likely due, in part, to the limited size of the natal home range and the relatively short duration of the post-fledging period. However, juveniles of all 3 species hatched from nests in areas of greater turbine density were more likely to die from predation or starvation just after fledging and prior to becoming independent compared to those in areas of lower turbine density. Taken together, these results suggest that wind turbines affected reproductive efforts by all 3 species to some degree, but these effects were greater for ferruginous hawks compared to the other 2 congeneric species. The causes of this negative association are unknown but likely represent some combination of breeding adults being killed from turbine collisions, disturbed from activities associated with the increasing wind energy development in the area, or displaced from portions of their home range to minimize the risk of disturbance or death. The potential for these effects necessitate that planning of future wind energy facilities be considered at larger geographic scales beyond the placement of individual turbines to limit development near raptor breeding areas. © 2016 The Wildlife Society.

The global potential for wind power generation is vast, and the number of installations is increasing rapidly. We review case studies from around the world of the effects on raptors of wind-energy development. Collision mortality, displacement, and habitat loss have the potential to cause population-level effects, especially for species that are rare or endangered. The impact on raptors has much to do with their behavior, so careful siting of wind-energy developments to avoid areas suited to raptor breeding, foraging, or migration would reduce these effects. At established wind farms that already conflict with raptors, reduction of fatalities may be feasible by curtailment of turbines as raptors approach, and offset through mitigation of other human causes of mortality such as electrocution and poisoning, provided the relative effects can be quantified. Measurement of raptor mortality at wind farms is the subject of intense effort and study, especially where mitigation is required by law, with novel statistical approaches recently made available to improve the notoriously difficult-to-estimate mortality rates of rare and hard-to-detect species. Global standards for wind farm placement, monitoring, and effects mitigation would be a valuable contribution to raptor conservation worldwide.