Building an Acoustic Lighthouse: Sounds to Steer Birds Away from Wind Turbines

By: Sam Mair

In future, the demand for wind energy is expected to increase as communities try to reduce their reliance on fossil fuels to supply electricity. While the transition to renewable energy is great news in terms of cleaner energy production, building more wind energy facilities also increases the risk of interactions between the turbines and wildlife. Eagles are of particular concern as deaths from collisions with wind turbines can diminish their already small populations. To prevent these interactions, auditory signal systems could be attached to wind turbines to warn birds such as eagles that there’s a hazard ahead; despite the size of wind turbines, the exact location of moving turbine blades can be hard for birds to pinpoint while flying. Goller and their team from Purdue University set out to design auditory signals that would best alert eagle species of wind turbines ahead under different types of environmental noise.

To design a signal to alert eagles of hazards ahead, the team first had to determine what types of sound were easiest for the eagles to detect. Focusing on two different eagle species, bald eagles and golden eagles, researchers placed each eagle in a box designed to eliminate environmental noise and then played different sounds over a speaker while monitoring the eagle’s brain activity. These alerts were then played with varying levels of background noise to assess if the eagles could detect the alerts in noisy environmental conditions. Static, unchanging sounds were easily detected by both golden and bald eagles but were much harder to separate from background noise. Dynamic sounds were less impacted by background noise, but the golden eagles showed less brain activity in response to these complex sounds. The reduced brain activity suggests that dynamic sounds wouldn’t effectively deter golden eagles from flying into wind turbines because the rapidly changing sound is hard for golden eagles to process.

The difference in golden and bald eagle’s ability to process dynamic sounds might be because they have different auditory filter widths. Auditory filter width refers to a tradeoff between their ability to distinguish similar frequency sounds and their ability to process rapidly changing sounds. A narrow filter means it’s easier to tell the difference between similar frequencies of sound but difficult to process quickly changing sounds because this species takes longer to make sense of what they hear. Species with a broad auditory filter width are better at processing sounds that change quickly but sounds of similar frequencies might sound the same. These differences in hearing ability may have evolved with differences in how the species communicate or detect predators or prey. Goller and their team think golden eagles likely have a narrower auditory filter width than bald eagles and recommend sounds of intermediate complexity for the alert signal since they were best detected by both species.

Even while focusing on only two bird species, the need for species specific auditory alert signals is already clear. Golden eagles responded to sounds differently than the bald eagles, and so the suggestion of an alert with an intermediate complexity sound is a compromise between the hearing ability of these two species. To design an optimal alert to reduce bird mortality from wind turbines, managers will have to consider which species are at risk in their area and use specific deterrent sounds to get the best result. The next step will be to assess intermediate complexity sounds as alert signals in a behavioral study to ensure it can redirect eagles from a hazard like wind turbines. After all, an acoustic lighthouse will only work if the travelers can “see” the warning signal.

Goller, B., Baumhardt, P., Dominguez-Villegas, E., Katzner, T., Fernández-Juricic, E., and Lucas, J.R. (2022) Selecting auditory alerting stimuli for eagles on the basis of auditory evoked potentials. Conservation Physiology. 10, coac059.