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Wind power development can affect entire raptor communities, not just individuals

Collisions with wind turbines are a documented threat to the lives of individual raptors. However, wind development also impacts the structure of nesting raptor communities, a discovery that could impact approaches to raptor conservation in the future.

This is according to a paper "Long-Term Changes in Nesting Raptor Communities After Construction of Wind Power Projects," in the Journal of Raptor Research. The research team confirms that several sensitive raptor species nesting along the border of Oregon and Washington, including Golden Eagles (Aquila chrysaetos), have decreased in abundance on wind power project sites. Other species, like Great-horned Owls (Bubo virginianus), have increased.

Raptors are more readily affected by wind energy than other birds in part because they utilize ridge-top soaring to save energy in flight, therefore encountering turbines at a higher rate. Wind projects also necessitate clearing of habitat which can attract raptor species that prefer hunting on open landscapes.

Thus far, most research on wind energy and raptors has focused on quantifying deaths from turbine strikes, improving turbine placement, and mediating collision risk. This research team underscores the narrow lens that this approach provides in terms of effects on communities of raptors.

Finding a dead raptor below a turbine offers no information about whether the individual was a local resident, a breeder, or a migrant—factors that influence population dynamics.

Lead author Jim Watson and his colleagues from the Washington and Oregon Departments of Fish and Wildlife, reviewed raptor surveys conducted prior to construction of 18 wind projects along the border of Oregon and Washington, and then repeated the same surveys on the same sites, post-construction.

They also surveyed four undeveloped sites in the area for reference on the composition of raptor communities at sites unaffected by wind power development.

The surveys focused on a variety of raptor species, including Golden Eagles, Ferruginous Hawks (Buteo regalis), Prairie Falcons (Falco mexicanus), Great-horned Owls (Buteo virginianus), and Common Ravens (Corvus corax). The latter are not raptors, but do compete with them for nest sites, and sometimes feed on raptor eggs and young, functioning ecologically as part of the raptor community in this part of their range.

The team found that Golden Eagles, Ferruginous Hawks, and Prairie Falcons, all of which breed in the study region, declined in abundance on project sites. This outcome aligns with the relative sensitivity of these species to anthropogenic change and underscores the reality that the nesting success of these species is compromised by wind development in this region.

Ravens and Great-horned Owls increased in abundance on project sites, likely affecting the dynamics for the other raptor species given their aggressive and adaptive behaviors.

The results of this study illuminate the value of long-term monitoring of raptors in areas with wind development and the importance of focusing study objectives on community composition.

"Most people are aware that there are tradeoffs for clean energy development, including the mortality of birds and bats from wind projects," says Watson.

"However, the consequence of mortality is often expressed through [the] loss or gain of total birds on a project after it is developed. Our research emphasizes the need to specifically consider effects on local breeding populations, particularly those of sensitive or declining species. Populations [that are] more common and adaptable can better compensate for impacts."

For sensitive species, wind projects are a contributing factor to an already challenging anthropogenic labyrinth that includes habitat conversion and declines in prey availability. Golden Eagles continue to suffer from lead contamination and Ferruginous Hawks have recently been uplisted to Endangered status in the State of Washington.

The research team envisions a shift away from focusing only on turbine collision fatalities to a more comprehensive research approach in which long-term surveys, before, during, and after wind project development become the norm. Raptor communities are dynamic. As top predators, raptors impact the health of their habitats in ecologically significant ways.

"Whether our concern is for Jackal Buzzards in Southern Africa, Brown Falcons in Australia, or Golden Eagles in the United States, the opportunity to effectively mitigate the effects of clean energy development on raptors must include long-term evaluation of breeding changes," says Watson.

He hopes to continue research that results in sound recommendations within the clean energy field and reduces damage to nesting populations of sensitive raptor species, an action he views as critical if those species are to remain in the skies for future generations to see.