Golden eagle eye looking down1/25/2024 Once data were collected, they developed a suite of audio test signals and worked with eagles at the Raptor Center to evaluate which of the signals generated the strongest response. The UMN research team studied raptors admitted to the university’s Raptor Center for treatment and worked with Sia: the Comanche Nation Ethno-Ornithological Initiative in Cyril, Oklahoma, to assess eagle hearing ranges. University of Minnesota: Eagles Can Hear Frequencies Ranging Across Four Octaves The Purdue research team concluded that these types of signals would be good candidates for further testing with bald eagles - but that deterrents for golden eagles should be complex tonal harmonics or modulated sounds that do not change very rapidly. In the presence of ambient noise, such as that of a wind turbine, sounds with rapid frequency or amplitude modulation were not as easily masked by the ambient noise.Bald eagles’ auditory systems were much better than golden eagles’ at processing complex sounds with dynamic, rapid changes in amplitude or frequency modulation.Both species responded strongly to tones between 0.5 kilohertz (kHz) and 5 kHz - roughly, the notes on the right half of a piano keyboard.Purdue researchers concluded that the auditory systems of bald and golden eagles were sufficiently different to warrant species-specific deterrent signals. Both species showed some level of adaptation to stimuli over time, indicating the need for additional, randomized visual and auditory signal testing. 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. Bald eagles showed a higher proportion of stress-related behavior to light-plus-sound signals. Furthermore, golden eagles exhibited a higher proportion of stress-related behaviors to visual signals than to sound or light-plus-sound signals. They identified candidate colors (blue/indigo and orange/red) that would be most visible to eagles against various backgrounds. The Purdue team also found that it is highly unlikely that golden or bald eagles can detect ultraviolet light. Illustration courtesy of Purdue University The Purdue University team found both species of eagles have a blind spot near the tops of their heads (bottom row). Visual field configurations of the golden eagle (left) and bald eagle (right). This finding supports the need for a deterrent that is sufficiently alarming to an eagle to cause it to look up when hunting. 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). The Purdue research team worked with seven raptor rehabilitation centers to evaluate eagle hearing and vision ranges. Purdue University: A Blind Spot Near the Top of Eagles’ Heads 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. 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. 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. 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. Findings from this research, which is funded by the Wind Energy Technologies Office (WETO), will be made available to eagle deterrent technology developers.īald eagles were removed from the endangered species list in 2007 after a strong population recovery. 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. University researchers examine eagle physiology to inform and improve eagle deterrents Sign up for daily news updates from CleanTechnica on email.
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