Digital Bioacoustics

It’s a crisp fall evening in Grand Teton National Park. A mournful, groaning call cuts through the dusky-blue light: a male elk, bugling. The sound ricochets across the grassy meadow. A minute later, another bull answers from somewhere in the shadows.

Bugles are the telltale sound of elk during mating season. Now new research has found that male elks’ bugles sound slightly different depending on where they live. Other studies have shown that whale, bat, and bird calls have dialects of sorts too, and a team led by Jennifer Clarke, a behavioral ecologist at the Center for Wildlife Studies and a professor at the University of La Verne, in California, is the first to identify such differences in any species of ungulate.

Hearing elk bugle in Rocky Mountain National Park decades ago inspired Clarke to investigate the sound. “My graduate students and I started delving into the library and could find nothing on elk communication, period,” she says. That surprised her: “Thousands of people go to national parks to hear them bugle, and we don’t know what we’re listening to.”

Her research, published earlier this year in the Journal of Mammalogy, dug into the unique symphony created by different elk herds. Although most people can detect human dialects and accents—a honey-thick southern drawl versus nasal New England speech—differences in regional elk bugles are almost imperceptible to human ears. But by using spectrograms to visually represent sound frequencies, researchers can see the details of each region’s signature bugles. “It’s like handwriting,” Clarke says. “You can recognize Bill’s handwriting from George’s handwriting.”

Pennsylvania’s elk herds were translocated from the West in the early 1900s, and today, they have longer tonal whistles and quieter bugles than elk in Colorado. Meanwhile, bugles change frequency from low to high tones more sharply in Wyoming than they do in Pennsylvania or Colorado.

Clarke isn’t sure why the dialects vary. She initially hypothesized that calls would differ based on the way sound travels in Pennsylvania’s dense forests compared with the more open landscapes of Colorado and Wyoming, but her data didn’t support that theory. Clarke hopes to find out whether genetic variation—which is more limited in Pennsylvania’s herd—might explain differences in bugles, and whether those differences are learned by young males listening to older bulls.

Clarke’s research adds a small piece to the larger puzzle of animal communication, says Daniel Blumstein, a biologist at UCLA who was not involved in the study. “It’s not as though a song or vocal learning is ‘all environmental’ or ‘all genetic,’” he says. “It’s an interplay between both.” Blumstein, a marmot-communication researcher, adds that the mechanisms behind these vocal variations deserve more study.

These unanswered questions are part of the larger field of bioacoustics, which blends biology and acoustics to deepen our understanding of the noises that surround us in nature. Bioacoustics can sometimes be used as a conservation tool to monitor animal behavior, and other studies are shedding light on how it affects animal evolution, disease transfer, and cognition.

Elk are not the only species with regional dialects. In North America, eastern and western hermit thrushes sing different song structures, and the white-crowned sparrow’s song can help ornithologists identify where it was born. Campbell’s monkeys also have localized dialects in their songs and calls, as does the rock hyrax, a mammal that looks like a rodent but is actually related to elephants.

Similar differences exist underwater, where whale songs have unique phrases that vary by location. Sperm whales in the Caribbean have clicking patterns in their calls that differ from those of their Pacific Ocean counterparts. Orcas in Puget Sound use distinctive clicks and whistles within their own pods.

Clarke also studies the vocalizations of ptarmigan, flying foxes, and Tasmanian devils. Her next research project will shed light on how bison mothers lead their herds and communicate with their calves. “They’re the heart of the herd,” she says. “What are they talking about?”