The mysteries of birdsong
Since early May, a distinctive eastern towhee has frequented my backyard in Charlotte. The typical song of this common species can be translated as “Drink your teeea!” This emphatic burst of notes ends with a trill. Sometimes the song is shortened to an assertive two-note command. “Drink tea!” The towhee in my backyard sounds as if he suffers from a stutter. To my ear, he seems to be saying, “Drink, drink, drink your tea!” Poor little fella, it seems he’s misplaced his trill.
Birdsong was once believed to be innate, but studies have proven that quite a bit of learning is involved. Early research concluded birds simply imitate the songs of their father and other nearby males. More recent work has shown that some birds have a lifelong ability to adapt their songs. This can give them an advantage in a variety of settings. Urban birds have been forced to tweak their songs so they can be heard over the din of the human environment. A study at University of California, Davis, found a common yellowthroat can sing up to 2,000 variations in a single day.
The common yellowthroat’s song is also known for its regional variations. These differences are known as dialects. According to Don Stap’s excellent and exhaustive book Birdsong, “Carolina wrens in Ohio sing their songs faster than Carolina wrens in Florida.” Apparently, Homo sapiens isn’t the only species that exhibits a Southern drawl.
Some birds in the United Kingdom develop a regional accent, just as humans do. Is this an indication of evolution at work?
In the United Kingdom, an effort is underway to document the regional dialects of the yellowhammer. This species occurs widely across the country, but individual birds tend to remain in the same location throughout their lives. These factors help produce a “thick” accent, just as they would in humans. If these dialects become too thick, experts believe the differences might affect a bird’s ability to breed with a partner from another area. This could eventually lead to the development of distinct sub-species. In fact, some scientists speculate regional variations in song could be an indication of evolution at work.
The Cornell Lab of Ornithology notes the towhee’s song sometimes begins with more than one “drink,” but I’ve never heard that variation in the Piedmont. (It’s also worth noting the example on their website, which was recorded in Maryland, sounds less melodious than our local birds.) Was the towhee in my backyard trying to distinguish himself from his rivals? Had a stranger come to town? Perhaps he was a juvenile who hadn’t yet nailed down his delivery? I posed these questions to bird guru John Gerwin, ornithologist at the N.C. Museum of Natural Sciences. He has heard towhees with a similar song in Raleigh – and observed that we don’t know nearly enough about towhee migration – but he agreed it could be a juvenile.
Stap addresses this issue. Soon after fledging, he says, birds begin to babble incoherently, like a human baby. This subsong, which often continues throughout the bird’s first summer, contains elements of the standard song, but they’re “jumbled and incomplete.” That’s a great description of the towhee in my backyard. Assuming the towhee survives the winter, Stap says, he’ll begin to practice again as the days grow longer, moving into a phase known as plastic song. By the time breeding season rolls around, he ought to be in command of his full song, signaling he’s ready to defend a territory and attract a mate.
The question remains: Why do birds sing? Is it only in service of procreation, or is it possible birds sometimes simply enjoy belting out a perfect song? In terms of evolution, that’s a risky behavior, an expenditure of valuable time and energy. Since birds can’t share their motives on a questionnaire, scientists have devised studies to measure levels of dopamine and opioids related to singing. (These neurochemicals are associated with satisfaction and pleasure.) Some results suggest birds do in fact experience an intrinsic pleasure from singing certain types of songs.
Until we know more, perhaps that question is best left to poets like Mary Oliver. In an interview with Krista Tippett on the podcast On Being, she discusses her admiration for the Sufi poet Rumi. Rumi once observed, “There are hundreds of ways to kneel and kiss the ground.” Toward the end of Oliver’s poem “I Happened to Be Standing,” she writes, “But I thought, of the wren’s singing, what could this be / if it isn’t a prayer?”
LISTEN TO THE EASTERN TOWHEE’S BIRDSONG
To hear examples of the eastern towhee’s song and calls, go to https://www.allaboutbirds.org/guide/Eastern_Towhee/sounds
Test your ability to visualize birdsong at https://academy.allaboutbirds.org/features/bird-song-hero/bird-song-hero-tutorial