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Eagle Ear: an Eye on How Raptors Hear

Peggy Nelson examines raptor hearing to prevent turbine collisions
April 13, 2018

“The projects I work on in the world of audiology are constantly changing, week to week, decade to decade,” says Professor Peggy Nelson. “Testing eagles for their hearing? Definitely unexpected, but not that surprising,” she laughs. 

A Space for Sensory Science

Nelson has had a large impact on the field of speech-language-hearing sciences (SLHS) nationally and at the U. She currently serves as the executive director of the Center for Applied and Translational Sensory Science (CATSS), a research center she helped launch in 2015. CATSS assists researchers with addressing sensory problems. 

“A few years ago, my colleagues in psychology and the SLHS department decided that what [CATSS] really needed was a multisensory research room.” Although both departments helped fund the construction, a generous grant from the U of M’s Office of the Vice President of Research made it possible. Housed in the basement of Elliott Hall, the multisensory perception lab has the newest research technology for stimulating senses, with a focus on audio-visual perception.  

Since its creation in 2016, the lab has been used by many U of M departments. Currently, there are 40 different research projects being conducted from 6 different colleges at the U. The multisensory perception lab has also directly impacted the projects Nelson has been working on, which brings us back to the birds. 

From People to Birds

What did Nelson and her team learn about eagle hearing?

In her own words, “Early results suggest that eagles may have somewhat less acute high frequency hearing sensitivity than some other birds.

"Further work is needed, but perhaps they are less reliant on hearing than vision for their survival.”

The Detection and Perception of Sound by Raptors project originally started out as a research venture about people. Nelson explains, “Sometimes being near a wind turbine gives people headaches or makes them dizzy. We were trying to figure out how to combat that.” 

The wind turbine research began after the University of Minnesota Twin Cities received a grant from Xcel Energy for the study because complaints were slowing down wind energy development. Nelson became passionate about this project, because as she states, “If human complaints are really holding back the development of further wind energy, then we should know about it.”  Working with engineers in the College of Science and Engineering’s St. Anthony Falls Lab, Nelson was able to create a machine that simulates what being around a wind turbine is like. 

A few months into the human testing, Nelson received a call from her colleague in the engineering department asking if she could test a bird’s reaction to wind turbines. “My first response was no,” Nelson recalls, “but he didn’t take no for an answer.” 

The Department of Energy had heard about Nelson’s wind turbine project and wanted to know how birds, specifically eagles, could be deterred from flying into wind turbines. Under various pieces of legislation, including the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act, it is illegal to kill an eagle either intentionally or incidentally. Although the wind turbines do not pose a risk great enough to potentially cause extinction, these birds are periodically killed by turbines. So, Nelson put the human wind turbine research on hold momentarily to enter the world of animal hearing. 

The  birds that were tested at CATSS as part of this project come from the Raptor Center, which each year cares for a few hundred eagles that have been injured. The U of M’s Raptor Center allowed Nelson the unique opportunity to conduct eagle research that would be otherwise off-limits due to the eagle’s protected species status. Eventually, most of the birds that are treated at the Raptor Center are released, but some lucky birds had the opportunity to enter the CATSS multisensory perception lab and be tested before going back into the wild. Admittedly, testing eagles is no small feat, so Nelson enlisted the help of volunteers and veterinary technicians, as well as Julia Ponder, executive director for the Raptor Center; Pat Redrig, co-founder of the Raptor Center; and Lori Arent, the clinic manager. 

“Testing eagles is surprisingly similar to testing babies,” explains Nelson. “You put the animal to sleep, hook up electrodes near their brain and their ears, play the sounds, and then read their brain activity.” Nelson and her colleagues from the Raptor Center are diving headfirst into this cutting-edge research project. Before these birds entered the endangered species list, the science to test them just did not exist. “Raptors, like eagles, have never been tested for their hearing abilities because they have been protected for so long,” she remarks. 

Limitless with SLHS

The ultimate goal of the research was to determine if there could be a way to create a noise that would deter eagles from flying near the wind turbines. Although Nelson and her team have concluded that this sort of mechanism is not likely, they had the unique opportunity to get a glimpse into how eagles talk, hear, and communicate. Their research has provided a lot of answers about the way birds, specifically eagles, perceive sound. 

Nelson comments, “I never thought I would be working with birds when I got into SLHS, but one of the cool things about this field is you never know.” Even working with wind turbines and human hearing was an out-of-the-ordinary experience for Nelson. As a researcher though, she is fascinated by these new experiences. Now that the raptor project has finished up, Nelson is excited to return to her original research query: how wind turbines affect humans. “I love coming to my job everyday,” Nelson adds, “because you never know when the phone rings what you might be up to do.”


This story was written by an undergraduate student account executive in CLAgency. Meet the team.