How would the proposed Humboldt offshore wind project affect birds and bats?

Marbled murrelet (Brachyramphus marmoratus). Source: OSU via Wikipedia (CC BY-SA 2.0) (2)

Relative to onshore and near-shore habitats, there are currently thought to be fewer bird and bat species that live in offshore ocean waters, and many studies are underway (1) to better understand use of the area and potential risks associated with offshore wind, with additional studies planned to last for the next several years in order to gain a fuller picture of the offshore ecosystem. Click here to view a map of GPS-marked birds that visited the Pacific Flyway between 2015 and 2023. As part of the offshore wind planning and permitting process, we are actually learning more about seabirds right now than we have ever known before.

Many winged species are thought to be at low risk from collisions because their flight patterns place them outside of the blade swept area (3) (the area of space that wind turbine blades move through), which begins several hundred feet above the ocean’s surface. Put simply, many avian species typically fly well below the turbine blades and will be at a very low risk of impact. A 2024 study (4) using a thermal tracker found that 79% of the birds tracked flew below the swept area of the hypothetical turbines. Other species, such as geese, are more likely (5) to fly at an altitude that puts them at risk of flying within this area, although it is currently unknown how they would react to the presence of turbines. In addition, some species are likely to simply avoid the turbines (6) by flying around them, as has been recorded in European offshore wind farms.

The National Audubon Society supports (7) responsibly-sited offshore wind energy projects because the benefits to species that are being impacted by climate change outweigh the potential direct harm to individual birds or bats. As seen on their website, under 1.5 degrees of warming only two Humboldt County (9) bird species are at high risk of extinction due to climate change, but under 3.0 degrees of warming, 40 species are. You can explore climate change impacts on their website here: Survival by Degrees: 389 Bird Species on the Brink (8).

A variety of studies have been conducted to monitor bird activity around wind turbines. As seen in this presentation (12) about a framework to evaluate collision vulnerability in future offshore wind developments (12) from the Schatz Energy Research Center at Cal Poly Humboldt in September 2024 (also updated in this scientific article (17), varying levels of seabird interaction can be found with rotor-swept zones (RSZ) depending on species and wind speed. See also the below figures illustrating findings of this study.

https://www.youtube.com/watch?v=KYf1p1Fq9KU

Video: Seabirds in 3D: A Framework to Evaluate Collision Vulnerability in Future Offshore Wind Developments.   (12)

Figure displaying probability of flying above 10m ASL dependent on wind speed for birds with different flight styles.

(2025 3D Framework from the Schatz Research Center) (17)

Density of birds off the North Coast compared to their density above 10m.

(2025 3D Framework from the Schatz Research Center) (17)

Recent studies in European countries show that the vast majority of migratory birds avoid wind turbines completely (18). A study by the German Offshore Energy Association (BWO) shows that “over 99.8% of migratory birds reliably [avoid] wind turbines”. A study at a Danish offshore wind farm found that the vast majority of migratory waterbirds avoid offshore turbines in their flightpaths, with radar tracking showing that 0.9% of waterbirds during the night and 0.6% of waterbirds during the day flew close enough to be at risk of collisions with the turbines. The map below shows the position of turbines (red dots) and the recorded bird flight paths (black lines) surrounding the wind farm. Another study involved the constant monitoring of a wind turbine and noted zero interactions with birds from a total of 2007 flight paths.

Flight trajectories during the initial operation of a Danish wind farm. Source: PubMed Central (Avian collision risk at an offshore wind farm) (15).

A 2026 radar study in Finland (21) also indicated adaptation to OSW infrastructure, with demonstrated tendency in waterbirds to navigate around turbines “at close range.” According to Lead Specialist at One Planet Amanda Pasanen, “monitoring of the local breeding bird population has shown no signs of negative effects at the population level.” Pasanen also noted that, while short-term effects appear to be negligible, ongoing monitoring is important to study long-term/indirect effects.

To further understand seasonal wildlife activity along the Pacific Coast, The Electric Power Research Institute (EPRI) are initiating a collaborative study that aims to establish baseline data on bat activity for offshore environments (14), submitted December 2024. They plan to measure up to 20 offshore sites utilizing long-term passive acoustic monitoring (PAM) alongside targeted telemetry for risks assessment. This data with help identify offshore areas where conditions favorable to bat presence are more common, allowing for further responsible offshore wind development.

For impacts to all species and ecosystems, we advocate for avoidance, minimization, and mitigation (AMM) — in that order — where the highest priority should be given to avoiding project impacts, then minimizing impacts that may occur, and finally mitigating impacts that do occur. The path forward for offshore wind does not have to clash with the survival and health of native bird populations. In a study by UC Santa Cruz’s Conservation Action Lab, scientists developed a framework for assessing impacts on bird populations and conducting proper mitigation for the scenarios in which avoiding and minimizing impacts are not possible (19). Offshore wind funding can be used for wildlife restoration in the project area that not only mitigates impacts but restores critical nesting grounds and habitat. Examples of mitigation that bolster bird populations are invasive species’ removal from breeding sites and reestablishment of colonies (19). Check out the Audubon's January 2025 report, Birds and Offshore Wind: Developing the Offshore Wind that Birds Need (13) to learn how offshore wind can protect North American bird species threatened by climate change. The report highlights the latest research, policy recommendations, and a science-based approach to developing offshore wind responsibly.

Here are some additional resources:

• Watch this video by U.S. Bureau of Ocean Energy Management (BOEM) seabird expert David Perekstra to hear a discussion of potential offshore wind impacts to seabirds in May 2023 (10).

• Click here to read more about potential impacts to seabirds due to floating offshore wind in California (11) from the California Ocean Science Trust in July 2024.

• Click here to see a fact sheet about Offshore Wind's impacts on migratory birds and bats (16).

References

1. Adams, J., Felis, J., Kelsey, E., and White, L. (2023, May 11). Marine birds of the California Current and studies to inform offshore renewable energy. California Coastal Commission. https://documents.coastal.ca.gov/assets/upcoming-projects/offshore-wind/Th4/Th4-Adams.pdf

2. Nelson, K. and Cushing, D. (2021, May 7). Marbled murrelet [Image]. Wikipedia. https://en.wikipedia.org/wiki/Marbled_murrelet#/media/File:Marbled_murrelet.jpg 

3. Bastawrous, M. (2015, May). Structural Dynamic Modeling of Wind Turbine Blades. Research Gate. https://doi.org/10.13140/RG.2.1.1965.9683

4. Schneider, S.R., Kramer, S.H., Bernstein, S.B., et al. (2024, April 24). Autonomous thermal tracking reveals spatiotemporal patterns of seabird activity relevant to interactions with floating offshore wind facilities. Front. Mar. Sci., 11. https://doi.org/10.3389/fmars.2024.1346758

5. Weiser, E.L., Overton, C.T., Douglas, D.C., et al. (2023, October 7). Geese migrating over the Pacific Ocean select altitudes coinciding with offshore wind turbine blades. Journal of Applied Ecology, 61: 951-962. https://doi.org/10.1111/1365-2664.14612

6. Desholm, M. and Kahlert, J. (2005, September 22). Avian collision risk at an offshore wind farm. Biology Letters, 1(3): 296-298. https://doi.org/10.1098/rsbl.2005.0336

7. Haney, J.C. (2023, March 10). What Offshore Wind Energy Can Teach Us About Seabirds. Audubon. www.audubon.org/news/what-offshore-wind-energy-can-teach-us-about-seabirds

8. ​Audubon. Survival by Degrees: 389 Bird Species on the Brink [Website] https://www.audubon.org/climate/survivalbydegrees/flyway/pacific

9. Audubon. Survival by Degrees: 389 Bird Species on the Brink, Humboldt County Page [Website] https://www.audubon.org/climate/survivalbydegrees/county?zipCode=95503

10. Pereksta, D.M. (2023, May 17). Birds and Offshore Wind Energy Development: BOEM’s Avian Study Strategy to Assess Data Needs and Effects [Video]. U.S. Bureau of Ocean Energy Management. https://drive.google.com/file/d/1JNJElljx0k3xcfXzrC_HgiW8BnbOWNdr/view

11. California Ocean Science Trust. (2024, July). Impacts to Seabirds. www.oceansciencetrust.org/wp-content/uploads/2024/07/OST-Science-Factsheet-3-Seabirds-Final.pdf

12. Schatz Energy Research Center. (2024, October 5). Seabirds in 3D: A Framework to Evaluate Collision Vulnerability in Future Offshore Wind Developments [Video]. YouTube. https://www.youtube.com/watch?v=KYf1p1Fq9KU

13. National Audubon Society. (2025, January). Birds and offshore wind: Developing the offshore wind that birds need https://www.audubon.org/our-work/climate/clean-energy/birds-and-offshore-wind-report

14. ​Establishing baseline data on BAT activity in the offshore environment: Developing tools and models to quantify risk of offshore wind energy development. Tethys. (2024, December 20). https://tethys.pnnl.gov/stories/establishing-baseline-data-bat-activity-offshore-environment-developing-tools-models 

15. Desholm, M., & Kahlert, J. (2005b, September 22). Avian collision risk at an offshore wind farm. Biology letters. https://pmc.ncbi.nlm.nih.gov/articles/PMC1617151/

16. American Clean Power. (2026, January). Wildlife and Windpower. https://cleanpower.org/wp-content/uploads/gateway/2025/03/ACP_WildlifeandWind_Fact-Sheet_0306.pdf

17. Schneider, Stephanie R. et al. (2025) SEABIRDS IN 3D: A FRAMEWORK TO EVALUATE COLLISION VULNERABILITY WITH FUTURE OFFSHORE WIND DEVELOPMENTS IN THE CALIFORNIA CURRENT SYSTEM https://www.marineornithology.org/PDF/54_1/54_1_215-240.pdf

18. Resnik, Diana. (2026). Two new studies could change critics’ opinions about how many birds die from wind turbines https://www.euronews.com/2026/04/11/two-new-studies-could-change-critics-opinions-about-how-many-birds-die-from-wind-turbines

19. Stephens, T. 2022. UC Santa Cruz. Offshore wind farms may harm seabirds, but scientists see potential for net positive impact. https://news.ucsc.edu/2022/11/offshore-wind-energy/

20. Offshore Bats. EPRI. https://www.epri.com/offshore-bats

21. Pasanen, et. al (2026). Hyoty Tuuli. Finland’s first bird radar study on offshore wind power: Tahkoluoto results suggest birds are adapting. https://hyotytuuli.fi/en/finlands-first-bird-radar-study-on-offshore-wind-power-tahkoluoto-results-suggest-birds-are-adapting/?utm_source=Tethys&utm_campaign=03a1c8f745-Tethys+Blast+19+December+2025_COPY_01&utm_medium=email&utm_term=0_-8ebb5ebe17-451631823