Wooing with Song and Mating for Life
The lyrics of nature's love songs are designed to win at love.
Posted Feb 12, 2018
For two individuals to fall in love, they must communicate. “Love begins in the eyes and ears. We fall in love through communication,” says neuroscientist Sarah Woolley of Columbia University’s Zuckerman Institute.
Woolley doesn’t actually study love among humans, but she studies mating in a distant relative — the zebra finch. These Australian finches make a good model for investigating what goes on in the brain during vocal learning. Just as humans have to learn speech early, songbirds must learn their song when they’re young. The subsequent romantic lives of the finches are interesting, too. As with almost every other species of songbird, only males sing. That song is produced by a specialized section of the brain that females don’t have. Both sexes, however, have specialized auditory systems, the better to hear the fine details of the song — the male so he can produce and perfect it, the female so she can judge it.
The particulars of the song have something to tell us about the role of communication in love. I asked Woolley to walk me through what has to happen for two of her finches to end up together.
Step One: Learn Your Song
The young male songbird needs a tutor, usually his father. “He memorizes the tutor’s song and so do his brothers, but then he improvises and changes the song,” Woolley says. “He does not produce an exact copy of his father’s song. In that way, brothers differentiate from each other and they differentiate from their father. Each male has own unique song by which the whole group identifies him. Then they sing the same song for the rest of their lives.”
This is no small feat. “They have an incredibly well-developed vocal organ, the syrinx. You’ve got to have an amazing brain to drive it,” says Woolley. “They can produce two totally different sounds at the same times from two sides of the syrinx. That’s why their songs are so amazing.”
There’s a deadline, however. “They become sexually mature at 90 days and something in the brain closes down the ability to learn song. It’s just this window in time in which they can learn. We call it a critical developmental period,” says Woolley. A male raised without a tutor will never sing well. “He develops what we call isolate song, a song that is highly impoverished. No female will have anything to do with him. She knows something went wrong in his upbringing.”
Step Two: Sing Your Heart Out
“Song is a courtship behavior,” says Woolley. “The two major functions of song in songbirds generally are attracting females and defending their territories or resources.” But zebra finches are highly social and live in colonies together, so they don’t need to defend territory. That leaves more time for courting females with song, says Woolley. “And he also does a little dance.”
Step Three: Listen for Complexity.
Females listen for variation in male songs. Some zebra finches have just four syllables in their songs, others as many as seven. “The female likes the song with seven syllables. She likes a complex song,” says Woolley. “We hypothesize it’s because males of higher quality sing more complex songs. It’s a sign of how well his brain functions. A bird with seven syllables produces a more complex song because he produces seven acoustically distinct sounds. The bird with four syllables is only producing four distinct sounds.” This is true in other songbirds with larger repertoires. Male song sparrows, for instance, have anywhere from eight to 16 song types in their repertoires. Bigger repertoires always get the girl.
Step Four: Choose Well.
Males will court just about anybody; females are the choosy sex. They analyze the quality of the male’s song and there’s a lot at stake. “Like humans, but unlike most other animals, both songbird parents raise the babies, both parents build the nest, incubate the eggs, feed the babies, teach the babies,” says Woolley. And most songbirds mate for life, which is usually seven or eight years. In the songbird world, they say divorce happens only by death.
The female is looking for a good partner, but also for a good tutor for any sons she might have. “The female is driven by natural selection to have her offspring be very successful in finding a mate and reproduce," Woolley says. "She chooses a male who’s going to teach her offspring the seven-syllable song. Song-learning accuracy is correlated with other cognitive skills in these birds. Because the male sticks around and shares the responsibility of raising the family 50-50, she’s choosing a male not just for genes but for his ability to find resources, to build the nest, to protect the nest.”
Step Five: Keep Singing, and Live Happily Ever After
For humans and songbirds, love doesn't just begin in the eyes and the ears (and the olfactory system, for humans); it stays there. Communication continues to matter. “Pair bonding, that’s what we call it in the songbirds and you could call it that in humans, occurs through communication and bond maintenance occurs through communication,” says Woolley. “What carries the communication into your brain are your senses and the parts of your brain processing that information are the sensory areas. By our life history, our genetic disposition, our early experience, our brains are tuned for communication signals that we will use to communicate with others. It’s critical.”
Woolley laughs. “I can show that scientifically in the birds. I can’t show it in people.”
Copyright: Lydia Denworth, 2018.