One January morning, Eric Rasmussen, an ornithologist was driving along the roads that line MPG Science and Conservation Ranch, near Victor, Montana. The snow quit falling just hours before. A fresh half-inch blanketed the older snow. Rasmussen pulled the truck over and parked in this forested draw. He noticed fresh mountain lion tracks. He grabbed his binos, bear spray, and backpack and began trudging off through the snow following the tracks for a half mile. He had a field note that he needed to complete that day and take some photos. The whole forest was quiet and not a creature was stirring.
Photo by Stephen Ransom
He stopped and listened a few times. Nothing. He kept following the game trail then three other, smaller lion cub tracks joined the larger cat’s trail. The four lion tracks lead down into this dark forested creek bottom. He scanned around with his binoculars and noticed a partially consumed and cached deer carcass with mountain lion tracks all around it. Rasmussen scoped out the area further with his binos and noticed the three cub’s tracks leading off uphill towards a large Douglas fir tree about 20 or 30 yards away that had dark, thick mistletoe consuming the bottom part of the trunk.
By this time, Rasmussen was really questioning what he was doing here? But he continued to stand there quietly for 20 minutes scanning everywhere for the mother lion. Then he heard a mountain chickadee give an alarm call — one single, nasally call note coming from the top of the mistletoe.
The reason the wooded areas had been all quiet, he realized, was because the chickadee had sent out a warning about the lioness’ whereabouts that all other prey animals in the vicinity had understood and quickly gone into hiding.
“I remember being uber aware of everything around me at that moment, a part of it all. I felt in tune with the potential of everything that could possibly happen in mother nature. I could be pounced upon at any moment. It was time to go but I also wanted to stay and be a part of it,” Rasmussen recalls.
Researchers like Rasmussen and others are discovering that animal language may not only be more advanced than we originally thought, but may even be comprised of sentences with nouns, verbs, and adjectives. Some of these nouns and adjectives are even understood across species.
“Birds understand “squirrelese” and squirrels understand “birdese,” says Dr. Erick Greene, a professor of biology at the University of Montana. Animals can also “encode” a lot of information in their alarm calls, such as threat level and the specific behavior of a predator. For instance, a squirrel can signal if a red-tail hawk is flying around with the intent of hunting or if it is just flying by. Scientists are finding that this information can travel incredibly fast and cover long distances. Many of these alarm calls are subtle, and most people don’t even notice the waves of information as they sweep by them in the forest.
Like Greene, Rasmussen is very keen on denoting much more fully the way this call of alarm crosses species, as well as how it starts off localized and how it specifically spreads through the forest. The call of alarm, researchers are finding, begins at a very localized point, announcing to other prey in the immediate vicinity that a specific predator is here. It then spreads like a tsunami of sound, propelling far out ahead of the predator.
Greene is presently studying bird language with the help of a mock predator. He had a taxidermist reconstruct several dead northern pygmy owls into mechanical birds of prey called “robo-raptors." Greene’s research team sets these birds up in an undisclosed coniferous forest of the Rockies, then watches the effects as they remotely control a stump to reveal the decoy. The “robo-owl” swivels its head and suddenly the birds in the yard hush. Then the yard erupts in a frenzy of sound as chickadees and red-breasted nuthatches flock and mob the owl announcing to all eavesdropping species, from red squirrels to mule deer, that there’s a predator.
Photo by Henry T. McLin
Studies by researchers like Greene and others are unveiling that mammals, birds, and even fish recognize alarm calls from other prey species. Researchers have found that many small birds catch the newswire of one species and take note. Squirrels, gophers, and other birds mimic these alarm calls to help broadcast the warning system. The mimicked calls are nearly identical acoustically. This chatter sweeps across hillsides, a sophisticated warning system that travels faster than a 100 miles an hour and precedes the predator by a few minutes.
Greene wants to decode the nuances of bird alarms and attempt to understand the “language of the forest.” He’s looking at this communication across large swaths of habitat.
Consider, he explains, the chickadee with their well-known call, “chick-a-dee.” When they make this call over and over they are compelling other birds to come harass and mob a predator until it departs. If they add additional “dees” to their “chick-a-dee” they are alerting others to the size of the predator. If it’s only one added syllable, then it means that it’s a large predator that doesn’t threaten them but threatens species closer in size. A northern pygmy owl weighs approximately 2.2 ounces and is 6.75 inches long. Whereas, a chickadee weighs about. 0.5 ounces and is 5.25 inches in height. This little owl can match the chickadees maneuverability through the forest and presents considerable danger to them. Because of this, chickadees will add an additional five to ten or twelve "dees"/syllables when they spot a pygmy owl. Squirrels, which are larger than the owl, continue eating pine cones and making squirrel middens, when they hear this specific call, but the nearby small songbirds, especially red-breasted nuthatches that flock with chickadees in the winter, immediately go into hiding. But it’s likely that if the squirrels hear the chickadees’ description for a northern goshawk, they would take notice.
These are the kinds of details that Greene, who is teaming up with researchers from the Cornell Lab of Ornithology for a three-year study, is hoping to pin down about this complex interspecies communication. They are sharing a $700,000 grant from the National Science Foundation with the primary aim of understanding bird language and what it means for conservation.
Greene is measuring these bird alarm calls with an acoustic microscope. They appear as a spectrogram, which essentially is a musical notation. On the screen, the signals look like a densely layered cake sitting on its side.
Dr Con Slobodchikoff, a biologist at Northern Arizona University, first used a similar instrument to decode prairie dog language. Slobodchikoff has pioneered research on prairie dog colonies in New Mexico by decoding their sophisticated language. He has studied Gunnison prairie dogs since the mid 1980s. Prairie dogs, like chickadees, use auditory cues to represent different predators.
Biologists have recorded the alarms while watching the predator’s behavior and the prairie dog’s response or escape and used computer analysis to search the acoustic structure of the alarm calls. The computer software generates a sonogram, which is a kind of pictorial representation of the frequencies and time values that are contained within a single vocalization. Each alarm call lasts a tenth of a second. Most calls are repeated numerous times. Based off of rigorous statistical methods, Slobodchikoff decodes the variability in a single chirp. A different key distinguishes a coyote from a domestic dog or a person.
Researchers experimented with this variability by having the same person walk out into a prairie dog colony in different colored tee shirts at different times of the day. The subsequent alarm calls contained size, shape, and color of clothes the person was wearing. (Prairie dogs have dichromatic vision, which means they only see blues, some greens and yellows, but no reds.) In some experiments, prairie dogs could even describe objects they had never seen before.
The alarm calls the scientists have decoded through computer software are composed of smaller units of sound like human phonemes — vowels and consonants. Each alarm call is like a human sentence with nouns, verbs, and adjectives. Nouns are the species, verbs are the activity, and the adjectives are the physical description of the signals. An example of this decoding of a prairie dog chirp from that experiment goes something like this: “A tall and thin, yellow (blonde)-haired person is running by wearing a green shirt, and blue pants.”
“There are even regional dialects among prairie dogs from say New Mexico compared to Arizona or Colorado, kind of like human dialects or different languages from different geographical areas,” Slobodchikoff said.
Prairie dogs also have social chatter that hasn’t been decoded yet by the scientists because they can’t tie some of the chatter to a specific behavior change during these vocalizations.
"This research shows that prairie dogs have the most sophisticated animal language that has been decoded so far,” Slobodchikoff told me via email. “However, as other scientists start looking at animal signals with respect to the context of those messages we will see other animals have just as sophisticated languages. I predict that we will find that other animals have even more sophisticated languages.”
Katie Sieving, a conservation ecologist at the University of Florida, has been doing similar research in deciduous woodlands on the East Coast with tufted titmice, a small songbird species that belongs to the tit and chickadee family that’s collectively called "paridae." These bird use a ‘seet’ note that they use to warn, which is at a higher frequency than what a raptor can hear. It’s almost a private channel. This call is given off when any bird is being attacked and other prey species, which can hear at the same frequency, take notice by ducking or hiding. Their other call the titmice make is a mobbing call that means essentially, ‘come hither and harass the predator until it is annoyed and departs.
Dozens of birds listen to tufted titmice. They are considered the forest’s crossing guards. Other birds will hold back from entering hazardous areas if they hear the alarm calls from these birds.
Photo by Ross Elliott
Over in the Tai forest in Côte d'Ivoire, psychologist Klaus Zuberbuhler studied the language of Diana monkeys and how they communicate with other species for a number of years. Zuberbuhler, who is based in Scotland, conducted an experiment where he carried a stereo out into the forest and played the roar of a leopard — Diana monkey’s most feared predators. Every time the monkey’s heard the roar, they screamed warning calls then ran up and climbed higher up the trees. When Zuberbuhler played crowned eagle shrieks, the Diana monkeys gave off a slightly different call and climbed lower in the trees to avoid attack from overhead.
Ten other species of monkeys that live in same forest seemed to understand the alarm calls of Diana monkeys and would climb up or down the trees depending on if the Dianas were calling out a leopard alarm or an eagle alarm.
But even as we are learning about how animals communicate across species, we are also learning about how manmade noise — noise from quarries, natural-gas development, factories, trains, airports, and automobiles are — are disrupting these critical communications. In the United States, for instance, studies show that over 80 percent of the land area now sits within two-thirds of a mile from a road.
To examine just how much human noise interferes with animal and bird communication, Dr Jesse Barber of Boise State University created a “phantom road” in a forest outside of Boise, Idaho that forest serves as an important resting spot for migrating birds during the fall. No road actually exists, but Barber and his team of researchers broadcast on speakers, the sounds of a busy highway that they can switch on and off. They found more than a one-quarter decline in bird abundance when the artificial road noise was turned on; some birds avoided the area almost entirely. In a 2013 study, Barber concluded that due to the noise of the mock road, these birds changed their behavior and decided to route through a quieter area.
“What we found was that they [the birds that did continue migrating here] had lower overall body condition and they gained significantly less weight when the road was ‘on,’ ” Barber says.
The impact of manmade noise has serious implications for migratory birds (as well as other animal species) that are in decline worldwide. One factor, in this decline of migratory birds might be due to artificial noises that hamper their ability to gather information such as warnings about danger and food sources and forces them to change their overall behavior. If birds can’t hear others warning of danger then they have to spend more time looking out and less time foraging. In the wintertime, birds have to gather enough calories to survive through the long, cold nights. This forces them to make a trade-off about gathering food and being vigilant. Alarm calls are a form of shared responsibility that serve to help keep others alive while others forage.
“Animal communication is much more complex than we ever imagined,” says Katie Sieving. “These components of the soundscape are evolutionarily important for a species to survive and these species have evolved together in these socially complex networks.”
Species like prairie dogs, chickadees, titmice, and Diana monkeys are purveyors of information passing out vital facts not just to their immediate kin groups, but also to whatever other species that may be eavesdropping. This is happening all across the planet with all life forms.
“I remember when I figured out how Twitter actually worked,” Sieving adds. “When I visited the page showing tweets emerging in real-time from every corner of the earth, it struck me how keenly useful information from others, freely available, can be. Well, the information generated by titmice and chickadee species across the globe is always trending in the communities where they live among — altogether — hundreds of warbler, vireo, woodpecker and other bird species that know the parid lingo. It’s the real twitter feed — the one that could mean a better meal for this woodpecker, or that a cardinal lives another day to visit your feeder.”
Before industrialization, people listened in on this language older than words that other animals speak. This newswire is all we had. In our self-created anthropocentric universe we began to think we had a monopoly on language. But now we are again beginning to realize how these nonhuman languages invisibly string the world together. Maybe if we quiet the human world a few decibels, we will hear many other things we’ve been missing from this intricate, vast interspecies communication web.
The next time a cacophony of sound washes over you in the forest, remember that the soundscape is full of languages that once kept you alive. Stop, listen, and observe. Tune in and try to decipher the messages that still resonate with meaning.