LINKED PAPER
Variation in flight characteristics associated with entry by eagles into rotor-swept zones of wind turbines. Rolek, B. W., Braham, M. A., Miller, T. A., Duerr, A. E., Katzner, T. E., McClure, C. J. W. 2024. IBIS. DOI: 10.1111/ibi.13264. VIEW

Wind farms are increasingly common across the globe, providing a cost-effective supply of renewable energy. Despite their benefits, a major concern of many people is their potential negative impacts on wildlife, such as through collisions with birds. One method to reduce wildlife fatality rates is automated curtailment, whereby individual wind turbines can be slowed or stopped in real-time when wildlife is considered to be at risk of collision, e.g. based on flight characteristics (Birdlife International, 2015). However, a high frequency of curtailments can reduce power generation, and it has been shown that many curtailments are unnecessary as the birds that trigger them never actually enter the rotor-swept zone where collisions with turbine blades can occur (McClure et al. 2021a).

In a recent study in Ibis, Brian Rolek and colleagues tested their prediction that flight characteristics that accurately forecast entry by eagles into rotor-swept zones vary among turbines, which would potentially open the door to using turbine-specific curtailment criteria to increase wind power efficacy while limiting fatal collisions.

Automated curtailment
The study was conducted at a wind-power facility in Wyoming, where automated curtailment of wind turbines using the machine vision system ‘IdentiFlight’ (IdentiFlight International, Louisville, CO, USA) has been shown to reduce the fatality rate of eagles (McClure et al. 2021b, 2022). First, an artificial intelligence system classifies nearby moving objects as eagles or non-eagles, and then automatic curtailments of wind turbines are triggered using a set of criteria based on the flight trajectories of the identified eagles. Previous research has shown that flight characteristics accurately forecast entry into rotor-swept zones (Rolek et al. 2022), but it is unknown if these characteristics vary among turbines. The researchers tested five flight characteristics as explanatory variables to predict probability of eagle entry into the rotor-swept zone: ALTITUDE (flight altitude); SPEED (speed of eagles); APPROACH (flying towards or away from nearest turbine); NORTH (whether a flight path was directed northward or southward); and EAST (whether a flight path was directed eastward or westward).

Figure 1. Associations between the probability of entering the rotor-swept zone in response to flight altitude of eagles (ALTITUDE) at Top of the World wind facility in Wyoming, USA. Thin lines depict means of individual turbines, and colours illustrate whether turbines were similar to the overall mean among turbines (yellow; Different = ‘No’) or had significant differences from the mean (purple; having a probability of direction ≥ 95%; Different = ‘Yes’). Thick line depicts overall mean among turbines.

Variation in rotor-swept zone entry flight characteristics
The results showed that speed, altitude, approach angle, and distance metrics associated with entry into rotor-swept zones can vary between turbines at this site, as predicted. It is noted that some unknown proportion of the flight paths analysed were of non-eagles (due to the machine vision system’s false classification rate), and that the act of curtailment itself might have affected an eagle’s flight behaviour, both of which may have impacted the modelled results and should be taken into consideration when interpreting the findings.

While the particular entry rates and their relationships with flight characteristics are site-specific, the finding that the relationship between flight characteristics and rotor-swept zone entry varies per turbine likely also applies to other wind-power facilities. Therefore, implementing turbine-specific curtailment criteria could help to reduce wildlife collisions of target species while better maintaining energy generation, ultimately helping to decrease the need for fossil fuels.

References

BirdLife International. (2015). Review and Guidance on Use of “Shutdown-on-Demand” for Wind Turbines to Conserve Migration Soaring Birds in the Rift Valley/Red Sea Flyway. VIEW

McClure, C.J.W., Rolek, B.W., Braham, M.A., Miller, T.A., Duerr, A.E., McCabe, J.D., Dunn, L. & Katzner, T.E. (2021a). Eagles enter rotor-swept zones of wind turbines at rates that vary per turbine. Ecology and Evolution 11: 11267–11274. VIEW

McClure, C.J.W., Rolek, B.W., Dunn, L., McCabe, J.D., Martinson, L. & Katzner, T.E. (2021b). Eagle fatalities are reduced by automated curtailment of wind turbines. Journal of Applied Ecology 58: 446–452. VIEW

McClure, C.J.W., Rolek, B.W., Dunn, L., McCabe, J.D., Martinson, L. & Katzner, T.E. (2022). Confirmation that eagle fatalities can be reduced by automated curtailment of wind turbines. Ecological Solutions and Evidence 3: e12173. VIEW

Rolek, B.W., Braham, M.A., Miller, T.A., Duerr, A.E., Katzner, T.E., McCabe, J.D., Dunn, L. & McClure, C.J.W. (2022). Flight characteristics forecast entry by eagles into rotor-swept zones of wind turbines. Ibis 164: 1–13. VIEW

Image credits

Top right: Wind Turbines and an old windmill at the Roscoe Wind Farm in West Texas | Matthew T Rader | CC BY-SA 4.0 Wikimedia Commons

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