University researchers examine eagle physiology to inform and improve eagle deterrents
Purdue University (Purdue) and the University of Minnesota (UMN) are studying the visual and auditory capabilities of bald and golden eagles to help improve the effectiveness of deterrents used around wind energy facilities. Findings from this research, which is funded by the Wind Energy Technologies Office (WETO), will be made available to eagle deterrent technology developers.
Bald eagles were removed from the endangered species list in 2007 after a strong population recovery. Golden eagles were not listed, but both eagle species are federally protected under the Bald and Golden Eagle Protection Act (BGEPA), which prohibits the killing (or “take”) of eagles, unless permitted. This act requires that wind energy developers and operators do everything they can to minimize risks to eagles through methods such as careful siting, deterrents, or sensors that monitor for incoming wildlife and shut down wind turbines if an eagle approaches.
One way to reduce risks is to develop technologies that produce sound or a visual cue to deter eagles from entering the airspace around wind turbines. To develop highly effective deterrents based on sound or visual stimuli to which eagles are most sensitive, Purdue University explored both eagle hearing and vision, whereas UMN researchers studied eagle hearing and identified possible surrogate species with hearing capabilities similar to bald and golden eagles.
Purdue University: A Blind Spot Near the Top of Eagles’ Heads
The Purdue research team worked with seven raptor rehabilitation centers to evaluate eagle hearing and vision ranges. They found that both bald and golden eagles have a blind spot near the tops of their heads (Figure 1) that hinders the birds’ ability to see a wind turbine ahead of them if looking downward (e.g., while hunting). This finding supports the need for a deterrent that is sufficiently alarming to an eagle to cause it to look up when hunting.
The Purdue team also found that it is highly unlikely that golden or bald eagles can detect ultraviolet light. They identified candidate colors (blue/indigo and orange/red) that would be most visible to eagles against various backgrounds. Furthermore, golden eagles exhibited a higher proportion of stress-related behaviors to visual signals than to sound or light-plus-sound signals. Bald eagles showed a higher proportion of stress-related behavior to light-plus-sound signals. In other words, golden eagles are more likely to respond to visual signals, whereas bald eagles are more likely to respond to a combination of sight and sound. Both species showed some level of adaptation to stimuli over time, indicating the need for additional, randomized visual and auditory signal testing.
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