They’re teenagers, and they’re off somewhere listening to music. Fortunately for Chris Templeton, these are song sparrows, so he can put radio transmitters on them to figure out where they go.
He’s guessing—remember he’s working with birds—that the young song sparrows have slipped off to go to school. Or to wherever it is in the shrubbery that they find tutors and learn to sing.
Lab studies show that song sparrows, and probably half of known bird species, have to learn the species-specific songs they need for communicating in romance or war. Birdsong, Templeton says, “is a really important model system for understanding how humans learn language.” The avian descendants of dinosaurs evolved their communication independently from people. So the aspects of learning that turned out the same, as well as those that turned out different, intrigue scientists studying the brain and language.
Birds learn songs, but there’s no evidence that other birds teach them—at least not in the human sense of doing something special, such as singing extra slowly in front of the chicks. Young birds do seem to listen to adults, though, and somehow end up learning a song from certain grown-ups while ignoring others.
A human might be tempted to conclude that finding the grown-up models would be easy, that a baby bird picks up the songs of its parent.
Don’t bet on it, Templeton says.
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Yet he and other song specialists are persevering. Lab work studied the pupils. Now it’s time to study the schools.
What’s to learn
Only a few animals need schooling to communicate with their own kind. Most of the trilling, roaring, squeaking and chattering out in the wild is instinctual and develops independent of teaching as animals grow up. So far biologists have found that the need to listen to experts to make intelligible sounds in the right context shows up only in certain birds, bats, primates and whales and their relatives.
Among primates, only people depend on learning for such a vital skill as producing sounds for communication. Even in birds, only some of the species learn. Plenty of parrots and hummingbirds do, and likewise many of what are called oscine songbirds, including the warblers, sparrows, blackbirds, thrushes and so on. In the past decade, some dogma-smashing research has shown that bellbirds, which don’t belong in any of the established groups of bird learners, pick up vocalizations distinctive to their home regions: quacks, whistles or a noise that bird-watchers transcribe as “bonk.”
Before getting to the question of where all these young learners pick up their communication skills, Jill Soha of OhioStateUniversity’s Borror Laboratory of Bioacoustics in Columbus points out that researchers are still sorting out what learning means among birds. This fall she’s writing up an experiment about what education does for grasshopper sparrows (Ammodramus savannarum).
Out in the wild, a neighborhood of grown-up males sounds like a grasshopper sparrow United Nations. Each male’s songs are recognizable as coming from its species: a few introductory notes and a long buzz. Each bird tweaks these elements, however, altering pitch, timing and other details into such variety that Soha can record a neighborhood’s songs and find no males singing tunes similar enough to suggest a shared tutor.
Yet grasshopper sparrows do need schooling of some sort. When Soha raised two youngsters in soundproof cages with no chance to hear an adult of their species, “they came up with weird songs,” she says. The birds buzzed, but sounded only marginally more like grasshopper sparrows than a kitchen appliance.
To see what learning pattern creates the diversity in adult song, Soha turned to a classic laboratory setup. She raised young birds in soundproof cages outfitted with loudspeakers broadcasting performances from different adult grasshopper sparrows.
In experiments like this in other species, such as the white-crowned sparrow, biologists in the middle of the last century came up with a basic scenario for how birds learn to sing. Before a youngster can make his own music, he needs to hear polished adult performances of his own species. (For many temperate birds, it really is his song. Females give short chirps and calls but don’t perform the more elaborate, learned arias.)
In this established scenario, a young bird hits an impressionable age, a phase of a month or two when he memorizes what grown-up songs sound like. As he learns, he starts singing what is apparently nonsense, like a human toddler baby-talking. Gradually he enunciates more precisely. As an adult, he can produce recognizable versions of a song or songs he heard as a little fellow. Just how long a bird’s impressionable phase lasts may depend on its species, with some kinds of birds picking up new songs throughout their lives.
When Soha broadcast adult song into the soundproof chambers of young grasshopper sparrows, they babbled. They slurred and lisped. Eventually they sang like grown-ups.
Their adult songs didn’t follow the old rules, though. When Soha compared the students’ final songs with the ones she had broadcast into their chambers, she found little resemblance. Several methods of comparing song similarity failed to agree on which student song derived from which tutor’s.
So the diverse field recordings, where Soha couldn’t find birds with the same tutor, meant that the species doesn’t use tutors as tightly as previously studied sparrows do. For these grasshopper sparrows, learning may be jazz, a matter of picking up a tune and then improvising. Or, Soha says, perhaps it’s closer to invention. It’s certainly not learning in the sense of accurate copying.
Even if they’re only going to improvise, hatchlings have to pick the right inspiration from among all the noises of nature around them.
A bird’s brain naturally seems to develop a partial template for the sound of its own species, Soha says. At least that’s the idea emerging from experiments so far. This template doesn’t provide the whole toolkit for developing proper songs, but it does guide a youngster in choosing what to learn.
What grabs a chick’s attention and says “Learn ME” may be some signal in the song itself. For white-crowned sparrows, at least part of the cue comes from the song’s opening whistle, Soha says. She has raised white-crowneds to mimic ground squirrel noises by incorporating a sparrow whistle in front of rodent recordings on a tutorial tape.
An entertaining minority of birds don’t stop with their own species when learning to vocalize. “When I had my first fawn-breasted bowerbird in my hand, it spewed out a series of ‘recordings’ as high in quality as the latest digital tape recording,” says John Endler of the University of Exeter in England. The bird gave high-fidelity imitations of other local birds, horses neighing and galloping, someone saying ‘morning, morning,’ even someone washing dishes.
For bowerbirds, males’ cross-species mimicry seems to appeal to females, but in general there’s little evidence so far of any benefit for birds that copy sounds of another creature, says Joah Madden, also at Exeter. “It could be just learning gone wrong,” he says.
Most birds grow up sounding like what they are—even where they are. Like people, birds can have dialects.
“Wawa,” says Tim Wright of New MexicoStateUniversity in Las Cruces. That’s what yellow-naped Amazon parrots (Amazona auropalliata) from northern Costa Rica squawk among themselves as they flock together. In 1996 he described a wawa border across the parrots’ range. South of the border, the parrots of the same species substitute wheep. And near the Nicaraguan border lies a third zone, where parrots call wuleep. Other vocalizations also change at these borders.
Wawa, wheep and wuleep parrot populations don’t show genetic differences, Wright says. The birds probably mingle and mate, and it’s learning that creates the dialect zones.
The border between the north and south hasn’t moved significantly in a decade, Wright says. He has revisited old study sites, the communal roosts where the parrots gather at night, and found mostly minor changes. Parrot dialects so far appear to be a long-term feature, much like human cultural differences, he and his colleagues report in the September Animal Behaviour.
To see how dialects might matter in bird society, Wright’s student Alejandro Salinas-Melgoza has been trying to move birds from one dialect zone into another, a challenging task. When he first moved adults with southern dialects some 30 kilometers into the northern zone, the birds immediately flew home.
He moved the next southern transplant farther, and a week later, brought a second bird to the same site. “Those southern birds linked right up and spent all their time together,” Wright says.
Last season went better as Salinas-Melgoza worked with a young, possibly female southerner. After the move, she began hanging around with the northerners. “Within six weeks she was using the northern dialect,” Wright says.
Wright had speculated that learning a new dialect arose from the need to fit in with a strange flock. Yet Salinas-Melgoza didn’t see any northern parrots attacking or cold-shouldering the immigrant with the funny accent.
One bird’s experience isn’t definitive, but Wright now muses that maybe courtship is what drives the learning of new dialects. Yellow-naped Amazon pairs sing duets, alternating his and her parts. Wright’s student Christine Dahlin has found that the parrots care about whether duets sound right, at least as far as syntax goes. When Dahlin broadcasts recordings that break common syntactical patterns, parrots ignore the loudspeakers. Maybe dialects matter too.
Even within a dialect group, singers have their quirks, and youngsters can shop around for their music models.
Male savannah sparrows (Passerculus sandwichensis) that gather each summer to breed on KentIsland in Canada’s Bay of Fundy sing the species’ short, buzzy songs with a distinctive island twang. Yet among those island breeders, Nathaniel Wheelwright can recognize individual males by variations in their songs.
To see how individuals develop their own songs, he and his students at BowdoinCollege in Brunswick, Maine, created a database of as many of the island song variations as they could. The team analyzed DNA samples to sort out the birds’ family relations. A few songs passed from father to son with little variation for at least four generations. But for most birds, the best match indicated a neighbor as the putative tutor. Only 12 percent of males (occupying their first territory) showed a strong influence from their social father’s music, the Bowdoin team and other collaborators report in the April Animal Behaviour. (See spectrograms on Page 24.)
Tutor choice intrigues Michael Beecher, who leads the research on song sparrows (Melospiza melodia) at the University of Washington. Males grow up to sing between six and 12 distinct songs. Beecher has tested various combinations of young song sparrows and possible mentors.
In one learning test, he placed each youngster beside an adult, but allowed the young birds to hear broadcasts of other tutor-tutee exchanges. When the youngsters started singing themselves, they turned out to have learned more of their songs by eavesdropping than by copying the guy singing right in their face, Beecher and colleagues reported in 2007.
Overheard songs’ allure supports Beecher’s idea that a critical part of learning is eavesdropping on musical discourse in a bird neighborhood and somehow picking among the songs in play.
Now Beecher and Templeton are analyzing results from their Seattle field project tracking young birds out listening to music. The experimental demands were “insane,” Beecher says. Starting in spring 2006, Templeton and his tracking team equipped young male birds with little radio tags. Thanks to the miracle of modern electronics, tags weighed only about 4 percent of the weight of a song sparrow. At that size, the batteries lasted only five or six weeks, necessitating trapping the youngster at the right time for a switch.
For a year, the crew went out every day to find young birds and record the songs of nearby adults. On a “perfect” day, data gathering took only five hours. The real world of evasive birds, cranky bystanders and suburban cats was far from perfect.
Young song sparrows move around more than he had expected, Templeton reported at the annual meeting of the Animal Behavior Society, held in August in Snowbird, Utah. Among the 15 young males he could track, each showed up in the territories of at least 20 adult males, making for exposure to some 200 songs.
For the young, eavesdropping is easy, Beecher says. He and his students used stuffed birds of various ages to mimic feathered bystanders hanging around adult male territories. Another grown-up male, albeit stuffed, elicited protests and attacks. But residents tolerated a (stuffed) teenager without a lot of fuss, sometimes flying off to do something more urgent before the researchers had clocked a full observation session.
Young males thus get a chance to watch territorial battles and check out neighborhoods where they could soon compete for their piece of real estate. The youngsters even seem attracted to the noisy conflicts of territorial grown-ups and fly closer as if eager to catch all the details.
Listening and learning songs from a variety of future neighbors could be good preparation for the rough-and-tumble music of the adult world. Seattle’s song sparrows don’t migrate, and males in the sedentary population have plenty of chances to get to know their rivals.
Males face off in territorial disputes by singing to each other, and Beecher has found that repeating a rival’s song back to him counts as a strong move. Learning a variety of the neighborhood songs could mean that a young male has his sassy comeback ready.
So for song sparrows that stay put year-round, choosing songs could be the first step in a world of musical warcraft. For other species, the dynamics differ, but the principle is the same: Song matters.
|“Plastic” song (October)||
|Crystallized song (May – 1/2)||
|Crystallized song (May – 2/2)||
LEARNING TO SING A song sparrow learns to sing gradually, just babbling subsong to himself in August. A few months later, he is able to perform song elements more precisely, in highly plastic arrangements, until his repertoire crystallizes in the spring.
Credit: C. Templeton