Raptor abundance declined near Oregon–Washington wind projects while common ravens increased

The death of the bird at the hand of the wind turbine takes only a few seconds.

However, making changes to the surrounding community takes years.

When studying the situation along the Columbia River of Oregon and Washington, researchers came back to survey the nesting bird community surrounding 18 wind-energy projects after about 18 years since their construction.

The most significant decreases came from those species that were identified as sensitive to human activities and changes in their natural shrub-steppe environment.

Fewer golden eagles, ferruginous hawks, and prairie falcons were found among the community.

On the contrary, there was an increase in common ravens.

Eighteen projects became one long experiment

In all, the study included wind farms located in the mid-Columbia River region within 25 miles of each other and consisting of eight project sites in Washington, nine project sites in Oregon, and one that extended beyond the study boundaries.

By 2021, there were a total of 1,723 turbines at 18 sites with an aggregate maximum capacity of 3,047 MW, covering 650 square miles.

The researchers compared pre-construction raptor-nest surveys against resurveying in 2020 and 2021.

This gap was different for each project site, extending up to 18 years in case of the oldest sites.

This is important, since one-year carcass survey can determine bird collision.

However, it cannot determine if the same species occupies nest areas after a generation.

Three sensitive hunters moved in the same direction

The most significant decreases came from those species that were identified as sensitive to human activities and changes in their natural shrub-steppe environment.

Golden eagles, ferruginous hawks, and prairie falcons were less numerous in terms of representation within the breeding community.

It appears that the decrease in the population of golden eagles was the most dramatic, followed by ferruginous hawks and prairie falcons.

However, the extent of the proportional decrease at wind project sites exceeded that observed at the reference sites by more than double.

This is the critical element.

It was not just the turbines that were the problem.

Four reference areas change the interpretation

The scientists also analyzed four undeveloped reference sites.

Sensitive raptors in such sites tended to be moving downwards as well, which can be explained by regional effects such as habitat loss, prey loss, and environmental degradation.

Therefore, the study does not claim all missing nests of eagles, hawks, and falcons in the studied sites were caused by wind energy.

The statement made in the study is more limited.

The decline in bird numbers was more pronounced in wind energy project landscapes compared to the reference landscapes, thus showing that the birds were under additional stress due to wind development.

However, the authors note that only four reference sites could be considered, therefore adding uncertainties into species-level analyses.

Ravens found the altered landscape easier

The common raven species showed the greatest number of nests increasing in abundance.

Unlike the three raptors, which were considered sensitive to turbines, common ravens increased significantly in both the wind project area and the reference sites, so the increase cannot be credited to turbines alone.

In fact, the paper suggests landfill areas and the development of electrical power infrastructure as reasons for raven increases in the region.

The landscape in wind projects includes human infrastructure, such as roads, among others.

Why are ravens important? Because they are more than just another entry in the bird counting list. They compete with raptors for nesting areas, raid food, and even kill eggs and juveniles of the prey species.

One of the adaptable predators, the great horned owl, also showed increasing trends.

The neighborhood changed its structure, not numbers of birds.

A turbine strike can empty more than one nest

The authors were able to monitor the specific ferruginous hawks’ and golden eagles’ territories to monitor yet another effect.

In some cases, the birds would die from colliding with the turbines, and then another bird would occupy the territory and die from colliding with another turbine.

Such losses can make a territory become what ecologists refer to as a population sink—a territory where animals keep coming but die faster than they can reproduce.

Other territories can stay unoccupied because new replacements simply refuse to visit this disturbed area at all.

That is why the authors speak about the need for such monitoring that will last significantly longer than the standard short-term post-construction fatality surveys associated with wind farms.

A dead bird under the first turbine shows individual mortality.

Nineteen years of nest surveys will show something else.

Turbines stayed put. Around them, the predator cast changed.

All the details of the study can be found here: Watson, J. W., Cherry, S. P., McNassar, G. J., Gerhardt, R. P., & Keren, I. N. (2025). Long-term changes in nesting raptor communities after construction of wind power projects. Journal of Raptor Research, 59(1), 1-14.