What can caribou hear? Scientists work to understand impact of noise

Researchers studying the hearing range of caribou have piloted a way to capture sounds the animals encounter.

The work lays the foundation for better understanding how noise from industrial developments may affect caribou, which could highlight ways to mitigate impacts.

Caribou are known to avoid infrastructure like roads, mines and pipelines. Some research also suggests those developments negatively affect the animals. Calves born closer to infrastructure have lower birth weights, a 2009 study in Alaska showed.

Although noise pollution is known to affect a wide variety of species, it’s still unclear how caribou respond to human-caused sounds.

“There’s a lot of confusion about it,” Megan Perra, a PhD student at the State University of New York College of Environmental Science and Forestry, told Cabin Radio.

Perra has been studying the hearing of European domesticated reindeer – reindeer and caribou are the same species, but are named reindeer in Europe or in North America if domesticated. In North America, wild reindeer are called caribou.

After a talk about her research at the Yellowknife Geoscience Forum on Wednesday, Perra said part of the uncertainty stems from previous work that showed the lower limit of reindeer’s auditory range is above the frequency of their vocalizations – meaning the animals wouldn’t be able to hear their own species’ vocalizations.

During her master’s at the University of Alaska Fairbanks, Perra decided to re-examine the sounds that reindeer (or caribou) can hear. At the time, the US government had just opened to oil and gas development a wildlife refuge in Alaska where caribou calve.

Perra focused her study on domesticated reindeer as they are easier to access and work with than caribou.

At a research station in Fairbanks, Perra and her colleagues built a sound booth in a barn. They then brought reindeer into the booth, two at a time.

“The reindeer get a little nervous when they are by themselves, so we had an emotional support reindeer next to the reindeer that was being tested,” she said.

The team then hooked up one of the reindeer to an electroencephalogram, a medical device used to measure brain activity, and held an earbud-like device next to its ear. While they played sounds of differing frequencies and volumes, researchers looked for a characteristic pattern of brain activity – an indicator that the animal was hearing the sound being played. The team repeated the test with six different reindeer.

They described their work in May in the Journal of Veterinary Behavior.

Sensitive to sounds

Reindeer pick up on a broad range of sounds, the researchers found. The animals responded to volumes equivalent to the hum of an empty room and frequencies at least as low as 30 hertz – the lowest the researchers could test with the equipment available.

“We weren’t really prepared for how sensitive they could be,” Perra said. Further research might reveal that reindeer can hear even lower-frequency sounds, she said.

Unlike previous work, the team found that the animals could indeed hear sounds of the same frequency as their vocalizations. The reindeer were also particularly sensitive to a high-frequency range that aligns with a clicking sound their tendons make as they snap over their ankle bones. “It’s an interesting coincidence,” Perra said. Although research on the subject is lacking, she suspects their sensitivity to these sounds may help keep herds together.  

The findings suggest that the animals’ sense of hearing plays an important role in helping them navigate through large landscapes and coordinate movements, according to Elie Gurarie, assistant professor of wildlife ecology at the State University of New York College of Environmental Science and Forestry. Gurarie was not involved in the study but is now Perra’s PhD supervisor.

The results also highlight that caribou can hear many non-biological sounds, the researchers reported, including those previously thought to be below their hearing range – like sounds related to seismic exploration.

The next step, they say, is figuring out how caribou respond to these sounds.

Listening in on caribou

Perra has been developing an approach to answer that question.

While in Alaska, she added audio recorders to caribous’ tracking collars. The recording device also contained an apparatus that gathered data on the animals’ movements, such as head shakes.

The recordings provide an intimate snapshot of the animals’ lives. In some recordings, for example, she captured caribou sleeping, drinking water and burping. In another, an aircraft can be heard flying overhead.

Tracking how caribou react to sounds in their environment could help define strategies for reducing development’s impact on the animals, according to Gurarie. If researchers knew exactly what caribou were responding to, he said, they could come up with concrete recommendations to mitigate the impacts of industry.

The audio collars could have applications beyond noise pollution, too. Gurarie and Perra think they might be useful for studying the impact of insect harassment, for example, which is notoriously hard to study and one of the possible reasons behind caribou decline.

Gurarie and Perra recently applied for funding to use audio collars to study caribou in the Northwest Territories and are now seeking to partner with communities. The direction of future work will depend on what communities want to know, they said.

Those interested in hearing more about the work can contact Perra by email.  

This article is produced under a Creative Commons CC BY-ND 4.0 licence through the Wilfrid Laurier University Climate Change Journalism Fellowship.