The Black-capped Chickadee is a cute and round little songbird familiar to denizens of the northern United States. It can often be seen in flocks, hopping around tree branches like a big puffy cotton-ball. As far as names go, the Black-capped Chickadee’s is fairly uncreative: the “Black-capped” part refers to the ‘cap’ of black feathers on the top of its head, and the “Chickadee” part is onomatopoeic, meant to mimic the sound of a unique call that all Chickadees produce. The call is instantly recognizable to anyone who’s heard it, immediately identifying the little friend who produced it. It’s also one of the more complex systems of animal communication discovered as of yet.
In the late 1980s, animal behaviorists Jack Hailman, Millicent Ficken, and Robert Ficken found that all ‘chick-a-dee’ calls produced by Black-capped Chickadees are composed of four discrete notes, arbitrarily designated ‘A’, ‘B’, ‘C’, and ‘D’ (the ‘A’, ‘B’, and ‘C’ notes constitute the ‘chick-a’ part of the call, while the ‘D’ note is the ‘Dee’ part). When producing a ‘chick-a-dee’ call, Black-capped Chickadees combine repetitions of the four notes to create hundreds of distinct permutations of the same call — akin to how people combine words to form sentences.
The ‘chick-a-dee’ call is remarkably sophisticated for such a tiny little bird. And at the time, this was the first instance of a recombinant system of animal communication ever discovered; when this was discovered the list of animals that combined small sounds to create a variety of messages doubled in size.
In their papers, Hailman, Ficken, and Ficken made a lot of lofty claims about Black-capped Chickadee calls constituting language. And in some places, linguists would probably agree — ‘chick-a-dee’ calls resemble language in the way arbitrary, discrete sounds are used to convey messages about the world, and of course in how they are combinatorial and therefore able to generate a theoretically infinite number of messages.
But Black-capped Chickadee calls lack many traits linguists believe to define language. For example, human languages are limited in their ability to discuss things by the imaginations of their speakers. But Black-capped Chickadees can likely only discuss specific topics that exist within their vicinity with their calls. Their communication is perhaps more akin to infinite variations of one sentence than it is to infinite sentences with distinct meaning. And crucially, Black-capped Chickadees can only combine their notes in ‘alphabetical’ order (so while call ‘A’ ‘A’ ‘B’ is fine, call ‘A’ ‘B’ ‘A’ is ungrammatical). In comparison, human syntax is hierarchical; words have roles — like “noun” or “verb” — not orders, and are grouped in sentences based on those roles. Sentences are formed of constituent groups of sounds that are lumped together from the top down. The Chickadee’s communication system is very sophisticated and interesting — but to call it language is perhaps inaccurate.
Of course, all this discussion of how Black-capped Chickadees communicate completely sidesteps the question of what they’re saying. That’s understandable, given that scientists can’t exactly ask these friends. The “chick-a-dee” call is used in a variety of contexts: it’s given by Chickadees that have discovered sources of food, by those that have been separated from their flock, given to call to mob a predator and as an “all-clear” signal when a predator has left. In all cases, it’s used as a sort of “come here” signal.
The strongest evidence about the semantics of Black-capped Chickadee calls comes from a 2005 study of the ‘chick-a-dee’ call as it is used to induce the mobbing of a predator. In the study, researchers presented a captive flock of Black-capped Chickadees with fifteen different species of live predators, and recorded the mobbing ‘chick-a-dee’ calls they produced.
“What we found is that they actually change a bunch of different features of their vocalizations based on how dangerous a predator is,” said Dr. Chris Templeton, the lead author of the study, in an interview with the Quest. In particular, his study found that the more dangerous a predator to Black-capped Chickadees, the more ‘Dee’ notes the call would generally contain. The Chickadees assessed the predators based on size and type — smaller, more agile raptors that could easily snatch a songbird from the sky elicited more ‘Dee’ notes than larger, less agile predators.
“We decided that ‘Dee’ is for danger,” said Templeton.
Templeton is an associate professor at Pacific University, where he still studies songbird communication and cognition. Right now, he’s researching how the Red-breasted Nuthatch, a small songbird species that likes to climb trees, decodes and relays information from ‘chick-a-dee’ alarm calls. According to Templeton, Red-breasted Nuthatches are one of over fifty different species that flock with Black-capped Chickadees and respond to their mobbing calls. But while Nuthatches understand and accurately respond to ‘chick-a-dee’ calls, they don’t trust them blindly.
“Chickadees have really reliable information about predator danger, but that’s subjective information,” Templeton said. “When [Red-breasted Nuthatches] hear Chickadees talking about these things, they behave as if they understand the difference, but don’t actually pass that information along.”
This contrast between how Nuthatches accurately respond to ‘chick-a-dee’ alarm calls and how they decline to propagate that information amongst themselves seems to indicate that they can make decisions about the reliability of information based on its source. While Nuthatch alarm calls accurately reflect the threat of predators they’ve seen with their own two eyes, they remain skeptical of unverified information acquired secondhand. “A lot of people would benefit from this kind of skepticism,” said Templeton.
This research challenges a commonly-held belief about mixed songbird flock: current scientific literature asserts that the “core” species of a mixed flock (in this case, the Black-capped Chickadee) is the sole distributor of information, and the “satellite” species that exist on the edges of the flock (such as Red-breasted nuthatches) eavesdrop on information without contributing anything. But this study demonstrates that Nuthatches pass on information in mixed flocks too. There is, in Templeton’s words, “Landscape-wide communication.”
“The closer we look at these systems, the more sophisticated we’re finding the information sharing is, the more sophisticated their cognitive abilities seem to be,” said Templeton.
When Hailman, Ficken, and Ficken were releasing studies on Black-capped Chickadees, their findings were largely unprecedented. At the time they wrote, “The ‘chick-a-dee’ calling of tits is the only manifestly combinatorial system of communication yet known in non-human animals.” Thirty years later, that’s not even remotely true. Sophisticated, combinatorial communication systems have been discovered by scientists studying Prairie Dog alarm calls, primates such as Campbell’s monkeys, humpback whales, and many other species of bird such as Japanese Great Tits and Southern pied babblers. It seems that natural selection is more favorable to complex, precise communication systems than Hailman, Ficken, and Ficken imagined.
But are they language? Templeton said it depends on how you define it. “We tend to define language in a human-centric way,” he said. “We often sort of write off these lowly animals as not being as clever as us, and maybe they’re not, but they’re more clever than we’ve historically given them credit for.”
Templeton continued, “For every part of language we define, there seems to be some animal that has it in their communication system, though we haven’t yet found an animal that has every feature of language.”
Even though Chickadees don’t have language, their communication system — and the communication systems of other animals — are extremely valuable in understanding human language. There are marked similarities, for example, between how some songbirds learn their songs and how humans acquire language; what could the way birds learn communication teach us about how we learn it?
“Language is something special, but it’s on this continuum,” Templeton says. And by studying the nuances of animal communication, we can learn more about ourselves.
But Black-capped Chickadee alarm calls don’t just have value because they can tell us something about ourselves — they have value by just existing, independent of what they can do for humans.
“Appreciating the world around us and understanding it is one of our basic needs in life,” says Templeton. “Understanding how sophisticated or complex animals are allows us to really appreciate them. Hopefully, that appreciation leads to action that will best promote their habitat and welfare and keeping nature as part of our life.”