The song of the American swamp sparrow
Do you like the songs that your great-great-great-grandparents danced to? Some birds apparently do.
In a study published this week, a Duke University researcher and his co-authors showed that American swamp sparrows may have sung the same songs for more than a thousand years. This shows that passing traditions on for generations isn’t unique to humans.
“The song types I hear in the morning are the same song types that the earliest European settlers would have heard,” said Duke biologist Stephen Nowicki, who co-wrote the study with a mathematician and a psychologist. “When the first European invaders came over 500 years ago, they heard what I was hearing just a week ago.”
Like baby humans, baby songbirds memorize syllables, or certain sounds, from adults around them. The researchers found that young swamp sparrows knew 13 syllables. But by the next spring, the birds narrowed their repertoire down to the three syllables they needed to sing as adults.
Humans do this process of overproduction and selective attrition, too — as babies we react to all languages, but as we grow older we lose the syllables we don't use in our native tongue.
The swamp sparrows sing almost exact copies of the most popular songs they hear as nestlings — like if you perfectly recited a kindergarten poem as an adult, and then your grandchildren recited almost the same poem.
“Very few animals learn to communicate the way humans learn to speak,” Nowicki said. “We know from experimental work that if you bring a baby bird into the lab and train them with recorded sound, they can copy them with remarkable accuracy. What we were showing was that, hey, that happens in a wild population with the same result.”
The researchers recorded 615 birds over six North American populations and classified 160 different syllable types from what they heard. They wrote a computer program to predict what syllables the birds would sing the following year. Then they ran the program 5,000 times and figured out what numbers they’d need to enter to get out today’s data, in which different populations sang very similar songs.
In the simulation, the oldest syllable type ended up 1,537 years old. For context, the fall of the Roman Empire was around 1,542 years ago.
Just over a quarter of all syllables were over 500 years old, and older syllables showed up more often than new ones. Innovative syllables turn obsolete quickly as swamp sparrows embrace more popular syllables.
But real life doesn’t exist in their computer program. The calculations tell us that under ideal circumstances, swamp sparrows can maintain very long traditions.
As a sanity check, the researchers compared swamp sparrow songs of today with recordings from the 1970s. Disco-era swamp sparrows sang 17 out of the 19 modern syllable types, and the most popular type then is still the most popular type now.
“It’s like the telephone game when you tell someone a sentence and they tell someone something else, and 10 times later it’s completely different,” Nowicki said. “What’s interesting is that a thousand times later, you still have the same syllable type in this population.”
The swamp sparrow traditions are impressive, said Barbara McRae, who writes a nature column for The Franklin Press in Western North Carolina, but it’s not clear how much you can compare birds with humans.
“It’s oral history swamp sparrow-style,” McRae said. “To be fair to humans, it’s just one little phrase they have to pass on. It’s easier than 500 years of begets and begots and all the stuff the Vikings passed down.”
While McRae is excited by the study, it doesn’t surprise other bird enthusiasts such as Kent Fiala, who runs the Carolina Bird Club website from Hillsborough.
“Certainly, birders know that each bird has a characteristic song and you can identify a bird just by hearing it without seeing it,” Fiala said. “You know what kind of bird sings that song, because they pass the song from generation to generation.”
Swamp sparrows have been singing the same songs for hundreds of years, which means that their culture rivals many human traditions in longevity.
“Something that we thought was really important about what makes us human, our ability to copy things precisely and maintain these long traditions, isn’t as critical as we thought,” Nowicki said. “These birds are doing it. It just means we have to ask in other dimensions, what makes us human?”
There’s not one single answer to that question, said Nora Carlson, biologist at the Max Planck Institute for Ornithology in Germany.
“I really like that more people are trying to break the ‘humans are special for these reasons and animals don’t do this’ idea,” Carlson said. “That one thing that makes us unique in the animal kingdom is probably how we combine all these behaviors. Every single time we find something that makes human different, we find an animal that does it. We have yet to find an animal that does all the things that humans do.”