Monkeys May Tune In to Basic Melodies
Bruce Bower
Some tunes stick in one's memory, sometimes with remarkable persistence. Think of "Happy Birthday," "Old MacDonald," and "Row, Row, Row Your Boat." In laboratory experiments, even infants exhibit a keen memory for such songs.
a3865_1733.JPG
Even if monkeys hear no evil, they may appreciate simple tunes.
Spike/PhotoDisk
A dozen of these childhood classics prove as memorable to rhesus monkeys as they do to people, a new study finds. This represents the first well-controlled demonstration that any nonhuman animal perceives simple melodies, say psychologist Anthony A. Wright of the University of Texas Medical School at Houston and his colleagues. Their report appears in the September Journal of Experimental Psychology: General.
"The perception of melodies depends on the structure of our nervous systems, not just on childhood and cultural experiences," Wright contends. "It's anybody's guess why this ability evolved in monkeys as well as humans."
Wright's group studied octave generalization, a critical facet of melody perception. In Western musical scales, moving from one eight-note octave to the next highest octave represents a doubling of acoustic frequencies. If a melody's other acoustic properties, such as its pitch patterns and its key, stay the same, people easily recognize the tune when it shifts by one or more octaves.
Two earlier studies, one in 1943 with rats and one in 1988 with dolphins, also yielded evidence of octave generalization. However, those efforts lacked definitive experimental controls, Wright holds. Several other tests, including some with monkeys and songbirds, found no evidence for octave generalization.
The new study focused on a pair of adult rhesus monkeys that learned to report whether one sound matched another heard after a 1-second delay. Sounds included a boat whistle, owl hoots, and sonar pings. If the sounds were the same, a touch to a loudspeaker on the right yielded a food pellet; if the sounds differed, a touch to a speaker on the left earned the prize.
Using this approach, both monkeys accurately identified repeats of any of 12 childhood songs—including those cited above—even when the melody shifted by one or two octaves. The monkeys succeeded whether the tunes sounded as if they'd been played on a piano, guitar, or other instruments.
The animals also displayed octave generalization for new melodies, created according to a mathematical formula for tonal, well-structured tunes. Tonality refers to the relationship of a melody's tones to a central tone, or key, that gives the passage a musical or songlike nature.
As previously reported for people's musical skills, the animals' ability to identify childhood songs plummeted when they heard tunes that shifted by either one-half octave or 1 1/2 octaves. In these trials, the monkeys touched the speakers randomly. Similar problems arose when they heard octave shifts of single notes, random sets of notes, or atonal sequences, in which there's no key.
"Wright's group makes a good case that these monkeys perceive whole tunes, not just isolated notes," remarks psychologist Sandra Trehub of the University of Toronto. Trehub, who studies infants' musical perception, theorizes that many mammals are sensitive to basic musical patterns.
Scientists have yet to reach a consensus on how to quantify the tonality of a sequence of musical notes, a concept that's crucial in the new study, comments psychologist Diana Deutsch of the University of California, San Diego. Although octave generalization probably occurs in nonhuman animals, Deutsch says the new experiments don't establish that monkeys perceive music.
domingo, 4 de noviembre de 2007
Music without Borders
Music without Borders
When birds trill and whales woo-oo, we call it singing. Are we serious?
Susan Milius
Luis Baptista—presumably—is not making this up. Especially not in a symposium at the annual meeting of the American Association for the Advancement of Science.
a2408_1342.JPG
The yellow warbler, other song birds, and whales are among the few vertebrates known to learn songs. A few others, such as gibbons, inherit their distinct tunes.
Still, the overflow crowd bursts out in giddy, slightly incredulous laughter.
Baptista, curator of ornithology and mammalogy at the California Academy of Sciences in San Francisco, has played a tape including one of the most recognizable phrases in Western music: "Ba-ba-ba baaahm." Baptista has primed his audience on what to listen for, but still a high-pitched version of the opening of Beethoven's Fifth Symphony rings out unmistakably.
Not. The notes come from a white-breasted wood wren in Mexico, Baptista tells the audience.
The bird and Beethoven sound astonishingly similar and represent one of the many convergences Baptista has found between music and birdsongs. At the February meeting in Washington, D.C., he described birds conforming to musical scales, improvising sonatas, even rewriting Mozart.
Common word choice tells the story, he argues. Frogs croak, dogs bark, wolves howl—but, Baptista notes, birds "sing." Such a happy overlap with music holds great promise for introducing people to the marvels of species diversity, Baptista urges.
Other researchers wring more significance from the convergences. Pioneering animal communications researcher Peter Marler of the University of California, Davis holds that for insights into the origins of music, the vocal behavior of birds will prove to be as profitable to study as that of monkeys and apes.
This attention to animal music arises with growing interest in a broader area called biomusicology. Biologists are collaborating with musicologists to ask what music is and how it evolved. The mix has raised far more questions than it has answered, but it's attracting new fans to composers with feathers, fur, and some really loud noises.
Animal noises
Think twice, though, before saying something crass like "animal noises" around pianist Patricia Gray of the National Musical Arts program. "We say 'musical sounds,'" Gray responds firmly.
Gray, who lives in Greensboro, N.C., has formed a coalition of about a dozen scientists and musicians under the auspices of the National Academy of Sciences. Through concerts and seminars, this BioMusic Project is "exploring the musical sounds of all species," she says.
So, does Gray accept a sparrow twitter as equivalent to her own keyboard artistry? "Why not?" she wants to know. "Why is it we go to other species with preconceptions of what our music means?"
Gray takes only the briefest pause before diving in to answer the blunt question, What is music?
When she was a college student, she recalls, composers were exploding conventions governing the sounds that could go into a musical piece. Compositions featured dissonances, fragments of speech, random noises, even John Cage's 4 minutes, 33 seconds of silence. The silent piece, 4'33", "was performed," Gray says, dodging the question of whether she, too, thinks silence is music. Out of this meltdown of musical tradition, Gray emerged with a spare definition. "Music is sound and time," she says. "Sound and time."
Gray's definition easily finds musicality in chirps, hoots, buzzes, and the myriad other acoustic phenomena of the living world. As a starting place for less liberal ears, however, she recommends avian music.
That works for music psychologist Diana Deutsch of the University of California, San Diego in La Jolla. She divides human sound communications into three loose groups: speech, music, and paralinguistic utterances such as laughs, screams, and groans. She likens the shrieks, yelps, and howls of many animals to that last category. However, "when we come to birdsong, with its elaborate hierarchical patterning, it seems that music provides a better analogy," Deutsch says.
Marler agrees that the majority of animal sounds will turn out to be "entirely emotional," although some communicate information about the outside world (SN: 9/12/98, p. 174). But he thinks that studies of whales and birds can contribute to the understanding of the origins of music.
Mozart's starling
Birds have earned the respect of some of the world's greatest musicians, Baptista says.
Mozart selected a starling as a pet and musical companion. The bird was an excellent choice, Baptista explains. Starlings pass down musical traditions, older males to younger males and older females to younger females. These birds mimic skillfully and abundantly—frogs, goats, and whistling shepherds.
Baptista cites a study of 80 wild starlings in France that turned up 105 imitations of other species. For starlings, music brings rewards. Females favor males that sing longer, more complex songs.
Mozart seems to have admired his avian companion's musical skills. One of his notebooks records a passage from the last movement of the Piano Concerto in G Major and the same passage as the starling revised it. The bird imitated it closely but changed the sharps to flats. "Das war schön"—That was beautiful!,— reads the comment in Mozart's hand.
When the starling died, Mozart held graveside ceremonies, singing hymns and reciting a poem he'd written for the fallen songster. Baptista agrees with two other ornithologists who have argued that Mozart's next composition, an odd sextet for strings and two horns, known as "A Musical Joke," shows starling style. Mozart wrote it only 8 days after the death of his bird, and it includes such starling-like bits as intertwined tunes, off-key recapitulations, and an abrupt ending.
Also, Baptista suggests new evidence for the starling's influence. He points out that starlings have the two-part syrinx, or voice organ, typical of songbirds and can belt out two songs at the same time. Baptista has even documented a starling simultaneously mimicking two birds—a grey fantail and a kelp gull—with the two sides of its syrinx. So, the final cadence of the sextet, essentially written in two keys played simultaneously, might honor the starling singing in two voices.
Mozart wasn't the only composer moved by birdsongs. Beethoven may have been such a fan that he plagiarized a motif from a contemporary feathered composer. Baptista plays the suspicious phrases, which form the lilting opening to the rondo of Beethoven's "Violin Concerto in D, Opus 61." A birder noted in 1953 that a European blackbird, a relative of U.S. robins, had come up with the same theme. Almost 30 years later, another sharp listener reported the same blackbird song. Both he and Baptista noted that generations of blackbirds seem to have preserved that tune, so perhaps it dated back to a time when Beethoven himself heard and borrowed it.
Avian orchestra
At least some of the enthusiasm for bird music comes from the sounds themselves, which lie so close to counterparts in the music of people. From ornithology recordings, Baptista conjures much of an orchestra. For oboe, for example, he selects the Australian diamond firetail finch, and for flute, he picks the long whistles of the white-bellied green imperial pigeon and the descending run of short notes uttered by the strawberry finch. He elects as bassoonist the common potoo, with a call that reminds him of the beginning of Mozart's clarinet quintet, albeit slightly off-key. He even finds an avian tuba: a western crowned pigeon of New Guinea booming out its courtship song.
Ornithologists have noted birdsongs pitched to the same musical scales used by people, Baptista points out. Wood thrushes can conform to the familiar Western diatonic scale; canyon wrens come close to the more complex chromatic scale, and hermit thrushes sing with the pentatonic scale of traditional Asian music.
Baptista can also summon from birds the rhythm and volume modulations that human composers employ: an accelerando in the wood warbler's windup, a swelling crescendo from the Heuglin's robin-chat, a fading diminuendo from the Swainson's thrush, and so on. Such musical phenomena as the borrowing of melodies, singing in duets or duels, and passing down traditions through families from generation to generation also show up in birds, Baptista reports.
a2408_2934.JPG
Name that tune: Which of these songs—or repeatable patterns in time—come from a whale, a human singer, a chestnut-sided warbler, Jean Pierre Rampal's flute? Sonograms show frequency rising vertically as time progresses horizontally. Answers at end of article.
Richard Horne, Spectrogram
Some species even compose in sonata form. A song sparrow, for example, belts out one of its themes, equivalent to a sonata's opening exposition, then fiddles with it a bit here and there much the way a nonfeathered composer develops a theme. The sparrow eventually burbles the original theme again, a version of a sonata's final recapitulation.
The similarity between bird and human sonatas is more than coincidence, Baptista argues. He recalls midcentury American aesthetician Charles Hartshorne proposing, "What stimulates animal organisms is change; what deadens response is sameness." This maxim governs people, too, Baptista says, and a composer's variations on a theme catch the attention through novelty.
However, unrelieved novelty eventually exhausts the perceiver, and a reference to the familiar relieves the fatigue. Birds and people share these reactions, Baptista argues, so he's not surprised that they also share composition strategies.
Inveterate composers
Humpback whales, too, are "inveterate composers," says Roger Payne of the Ocean Alliance in Lincoln, Mass., after 3 decades of oceanic listening. The most musicianlike of the whales, male humpbacks sing while cruising around their summer breeding grounds or migrating. The loud, wavering songs string together several repeated phrases or themes, and one whale's session of song after song can stretch more than 24 hours.
Males change their songs as the months pass. All the males in the same ocean sing basically the same tunes, even though the current hit takes some time to travel. "There seems to be no limit to what they can come up with. It's just that they get there by modifying existing sounds rather than by creating them de novo, as is our habit," Payne observes.
Whatever the process, humpbacks sing in patterns that Payne calls "strikingly similar" to human musical traditions. He detects rhythms, phrases that last just a few seconds, song lengths ranging between those of human ballads and symphonic movements, and percussive elements as an occasional emphasis in longer strains of pure tones. Even though a whale can woo-oo over at least seven octaves, Payne finds that it combines notes that have wavelength relationships familiar to people's ears.
Most surprising, says Payne, is the discovery that humpbacks use rhymes. "When someone speaks in a language you don't understand, you still know when they are reciting poetry," he argues. Among whales, a particular sound repeats at relatively regular intervals.
These rhymes may be for whales just what moon, spoon, and June do for human crooners, suggest Linda Guinee and Katy Payne of Cornell University. For a long concert during breeding season, the rhymes may help the performer remember what comes next. When Guinee and Payne checked for rhymes in simple and elaborate humpback songs, the complex ones were much more likely to rhyme.
Although primates are closer to Pavarotti than a whale is, they aren't particularly musical, notes Thomas Geissmann of the Institute of Zoology in Hannover, Germany. In his work on evolution, he accepts as a song a string of notes, usually of more than one type, that form a recognizable pattern in time. Some 26, or 11 percent, of primate species sing by this definition, he reports in The Origins of Music (2000, N.L. Wallin et al., eds., MIT Press). The chanteurs include some of the indris, tarsiers, titis, and gibbons. The behavior seems to have evolved independently four times within primates, he says.
Animal communication
Scientists who have focused their careers on animal communications vary widely in their opinions on the parallels between twitters and tunes.
Eugene Morton, an ornithologist at the Smithsonian Institution in Washington, D.C., and a BioMusic member, applauds the project's efforts to tout the marvels of birdsongs as markers of biodiversity. However, he turns almost stern at the question of whether those sounds are really songs dressed up in feathers.
"Any analogy to human music is not interesting to me," Morton says. "It doesn't explain anything about how the world is, except how humans want to perceive it. Good on 'em, but I want to understand animals."
From a bird's perspective, he argues, song is either "territorial defense or mate attraction, but in both cases it's very-long-distance communication." His 1992 book Animal Talk (Random House) expounds the idea that vocal traditions constitute an avian broadcasting network, letting birds minimize the arduous work of flying about during interactions.
"That's where I think it differs from human music," he says. "Human music isn't particularly distance related."
Entomologist Thomas Eisner of Cornell University likewise draws a distinction between enjoying animal sounds and saying that animals make music.
He remembers Payne bringing him the first recording of humpback whale sounds. "He insisted that we both have a glass of wine before we listened to it," Eisner recalls. "We went to the studio, we put on earphones, and I was sent into outer space."
As an accomplished keyboard player, Eisner says, "If a whale calls me up tomorrow and wants to do an evening of sonatas, I would be the first to volunteer."
Do the whales, however, perceive their sounds as sweet music? "It's an untestable question in scientific terms," he says. "The sense of inner tranquility that I personally get out of listening to the Goldberg Variations I can't test for. I can't even test for it in another human being."
Nonetheless, lobster specialist Jelle Atema of Boston University, who has played flute to Eisner's accompaniment, acknowledges some similarities between human music and animal utterances. "Birds, too, learn their songs and use them to be known and attractive in their social environment," Atema explains. "Males sing. Other males hate them for it and try to sing louder, better, longer to impress the other sex.
"I bet that the effects of all these vocalizations are measurable in hormonal responses that alter the behavior of the listener," Atema says. "And here we may be similar to animals. Galina Vishnevskaya need only sing one note, and she pierces my heart."
Psychologist Carol Krumhansl of Cornell University suggests looking for similarities in perceptions of sound sequences. Her work with music, such as the strings of syllables known as yoiks in Finland, has suggested regularities in the way people learn what to expect next in a melody. She raises the question of whether other species have similar expectations.
In the end, speculating about animal sounds and their effects may tell us mostly about ourselves, says Atema. "All we can do scientifically is to measure our noises, catalog them, analyze their components and structure, and then do the same for animal noises," he says. "'Splitters' will then decide that humans are demonstrably different from animals and thus animals do not have music. 'Lumpers' will see many similarities and conclude from the same data that we all have a lot of music in common."
In all the theorizing over the nature of music, Baptista urges listeners to remember the plight of the musicians. A quail species that Beethoven, Schubert, and Haydn all echoed in their compositions has disappeared in parts of Europe, he laments. The Soccorro mockingbirds, which sing in counterpoint, are losing habitat to sheep.
Beyond all the acoustical analysis, Baptista says, "part of the magic of a bird's song is found in the miracle of the bird itself."
From Science News, Vol. 157, No. 16, April 15, 2000, p. 252.
Fuente:
http://www.sciencenews.org/articles/20000415/bob11.asp
When birds trill and whales woo-oo, we call it singing. Are we serious?
Susan Milius
Luis Baptista—presumably—is not making this up. Especially not in a symposium at the annual meeting of the American Association for the Advancement of Science.
a2408_1342.JPG
The yellow warbler, other song birds, and whales are among the few vertebrates known to learn songs. A few others, such as gibbons, inherit their distinct tunes.
Still, the overflow crowd bursts out in giddy, slightly incredulous laughter.
Baptista, curator of ornithology and mammalogy at the California Academy of Sciences in San Francisco, has played a tape including one of the most recognizable phrases in Western music: "Ba-ba-ba baaahm." Baptista has primed his audience on what to listen for, but still a high-pitched version of the opening of Beethoven's Fifth Symphony rings out unmistakably.
Not. The notes come from a white-breasted wood wren in Mexico, Baptista tells the audience.
The bird and Beethoven sound astonishingly similar and represent one of the many convergences Baptista has found between music and birdsongs. At the February meeting in Washington, D.C., he described birds conforming to musical scales, improvising sonatas, even rewriting Mozart.
Common word choice tells the story, he argues. Frogs croak, dogs bark, wolves howl—but, Baptista notes, birds "sing." Such a happy overlap with music holds great promise for introducing people to the marvels of species diversity, Baptista urges.
Other researchers wring more significance from the convergences. Pioneering animal communications researcher Peter Marler of the University of California, Davis holds that for insights into the origins of music, the vocal behavior of birds will prove to be as profitable to study as that of monkeys and apes.
This attention to animal music arises with growing interest in a broader area called biomusicology. Biologists are collaborating with musicologists to ask what music is and how it evolved. The mix has raised far more questions than it has answered, but it's attracting new fans to composers with feathers, fur, and some really loud noises.
Animal noises
Think twice, though, before saying something crass like "animal noises" around pianist Patricia Gray of the National Musical Arts program. "We say 'musical sounds,'" Gray responds firmly.
Gray, who lives in Greensboro, N.C., has formed a coalition of about a dozen scientists and musicians under the auspices of the National Academy of Sciences. Through concerts and seminars, this BioMusic Project is "exploring the musical sounds of all species," she says.
So, does Gray accept a sparrow twitter as equivalent to her own keyboard artistry? "Why not?" she wants to know. "Why is it we go to other species with preconceptions of what our music means?"
Gray takes only the briefest pause before diving in to answer the blunt question, What is music?
When she was a college student, she recalls, composers were exploding conventions governing the sounds that could go into a musical piece. Compositions featured dissonances, fragments of speech, random noises, even John Cage's 4 minutes, 33 seconds of silence. The silent piece, 4'33", "was performed," Gray says, dodging the question of whether she, too, thinks silence is music. Out of this meltdown of musical tradition, Gray emerged with a spare definition. "Music is sound and time," she says. "Sound and time."
Gray's definition easily finds musicality in chirps, hoots, buzzes, and the myriad other acoustic phenomena of the living world. As a starting place for less liberal ears, however, she recommends avian music.
That works for music psychologist Diana Deutsch of the University of California, San Diego in La Jolla. She divides human sound communications into three loose groups: speech, music, and paralinguistic utterances such as laughs, screams, and groans. She likens the shrieks, yelps, and howls of many animals to that last category. However, "when we come to birdsong, with its elaborate hierarchical patterning, it seems that music provides a better analogy," Deutsch says.
Marler agrees that the majority of animal sounds will turn out to be "entirely emotional," although some communicate information about the outside world (SN: 9/12/98, p. 174). But he thinks that studies of whales and birds can contribute to the understanding of the origins of music.
Mozart's starling
Birds have earned the respect of some of the world's greatest musicians, Baptista says.
Mozart selected a starling as a pet and musical companion. The bird was an excellent choice, Baptista explains. Starlings pass down musical traditions, older males to younger males and older females to younger females. These birds mimic skillfully and abundantly—frogs, goats, and whistling shepherds.
Baptista cites a study of 80 wild starlings in France that turned up 105 imitations of other species. For starlings, music brings rewards. Females favor males that sing longer, more complex songs.
Mozart seems to have admired his avian companion's musical skills. One of his notebooks records a passage from the last movement of the Piano Concerto in G Major and the same passage as the starling revised it. The bird imitated it closely but changed the sharps to flats. "Das war schön"—That was beautiful!,— reads the comment in Mozart's hand.
When the starling died, Mozart held graveside ceremonies, singing hymns and reciting a poem he'd written for the fallen songster. Baptista agrees with two other ornithologists who have argued that Mozart's next composition, an odd sextet for strings and two horns, known as "A Musical Joke," shows starling style. Mozart wrote it only 8 days after the death of his bird, and it includes such starling-like bits as intertwined tunes, off-key recapitulations, and an abrupt ending.
Also, Baptista suggests new evidence for the starling's influence. He points out that starlings have the two-part syrinx, or voice organ, typical of songbirds and can belt out two songs at the same time. Baptista has even documented a starling simultaneously mimicking two birds—a grey fantail and a kelp gull—with the two sides of its syrinx. So, the final cadence of the sextet, essentially written in two keys played simultaneously, might honor the starling singing in two voices.
Mozart wasn't the only composer moved by birdsongs. Beethoven may have been such a fan that he plagiarized a motif from a contemporary feathered composer. Baptista plays the suspicious phrases, which form the lilting opening to the rondo of Beethoven's "Violin Concerto in D, Opus 61." A birder noted in 1953 that a European blackbird, a relative of U.S. robins, had come up with the same theme. Almost 30 years later, another sharp listener reported the same blackbird song. Both he and Baptista noted that generations of blackbirds seem to have preserved that tune, so perhaps it dated back to a time when Beethoven himself heard and borrowed it.
Avian orchestra
At least some of the enthusiasm for bird music comes from the sounds themselves, which lie so close to counterparts in the music of people. From ornithology recordings, Baptista conjures much of an orchestra. For oboe, for example, he selects the Australian diamond firetail finch, and for flute, he picks the long whistles of the white-bellied green imperial pigeon and the descending run of short notes uttered by the strawberry finch. He elects as bassoonist the common potoo, with a call that reminds him of the beginning of Mozart's clarinet quintet, albeit slightly off-key. He even finds an avian tuba: a western crowned pigeon of New Guinea booming out its courtship song.
Ornithologists have noted birdsongs pitched to the same musical scales used by people, Baptista points out. Wood thrushes can conform to the familiar Western diatonic scale; canyon wrens come close to the more complex chromatic scale, and hermit thrushes sing with the pentatonic scale of traditional Asian music.
Baptista can also summon from birds the rhythm and volume modulations that human composers employ: an accelerando in the wood warbler's windup, a swelling crescendo from the Heuglin's robin-chat, a fading diminuendo from the Swainson's thrush, and so on. Such musical phenomena as the borrowing of melodies, singing in duets or duels, and passing down traditions through families from generation to generation also show up in birds, Baptista reports.
a2408_2934.JPG
Name that tune: Which of these songs—or repeatable patterns in time—come from a whale, a human singer, a chestnut-sided warbler, Jean Pierre Rampal's flute? Sonograms show frequency rising vertically as time progresses horizontally. Answers at end of article.
Richard Horne, Spectrogram
Some species even compose in sonata form. A song sparrow, for example, belts out one of its themes, equivalent to a sonata's opening exposition, then fiddles with it a bit here and there much the way a nonfeathered composer develops a theme. The sparrow eventually burbles the original theme again, a version of a sonata's final recapitulation.
The similarity between bird and human sonatas is more than coincidence, Baptista argues. He recalls midcentury American aesthetician Charles Hartshorne proposing, "What stimulates animal organisms is change; what deadens response is sameness." This maxim governs people, too, Baptista says, and a composer's variations on a theme catch the attention through novelty.
However, unrelieved novelty eventually exhausts the perceiver, and a reference to the familiar relieves the fatigue. Birds and people share these reactions, Baptista argues, so he's not surprised that they also share composition strategies.
Inveterate composers
Humpback whales, too, are "inveterate composers," says Roger Payne of the Ocean Alliance in Lincoln, Mass., after 3 decades of oceanic listening. The most musicianlike of the whales, male humpbacks sing while cruising around their summer breeding grounds or migrating. The loud, wavering songs string together several repeated phrases or themes, and one whale's session of song after song can stretch more than 24 hours.
Males change their songs as the months pass. All the males in the same ocean sing basically the same tunes, even though the current hit takes some time to travel. "There seems to be no limit to what they can come up with. It's just that they get there by modifying existing sounds rather than by creating them de novo, as is our habit," Payne observes.
Whatever the process, humpbacks sing in patterns that Payne calls "strikingly similar" to human musical traditions. He detects rhythms, phrases that last just a few seconds, song lengths ranging between those of human ballads and symphonic movements, and percussive elements as an occasional emphasis in longer strains of pure tones. Even though a whale can woo-oo over at least seven octaves, Payne finds that it combines notes that have wavelength relationships familiar to people's ears.
Most surprising, says Payne, is the discovery that humpbacks use rhymes. "When someone speaks in a language you don't understand, you still know when they are reciting poetry," he argues. Among whales, a particular sound repeats at relatively regular intervals.
These rhymes may be for whales just what moon, spoon, and June do for human crooners, suggest Linda Guinee and Katy Payne of Cornell University. For a long concert during breeding season, the rhymes may help the performer remember what comes next. When Guinee and Payne checked for rhymes in simple and elaborate humpback songs, the complex ones were much more likely to rhyme.
Although primates are closer to Pavarotti than a whale is, they aren't particularly musical, notes Thomas Geissmann of the Institute of Zoology in Hannover, Germany. In his work on evolution, he accepts as a song a string of notes, usually of more than one type, that form a recognizable pattern in time. Some 26, or 11 percent, of primate species sing by this definition, he reports in The Origins of Music (2000, N.L. Wallin et al., eds., MIT Press). The chanteurs include some of the indris, tarsiers, titis, and gibbons. The behavior seems to have evolved independently four times within primates, he says.
Animal communication
Scientists who have focused their careers on animal communications vary widely in their opinions on the parallels between twitters and tunes.
Eugene Morton, an ornithologist at the Smithsonian Institution in Washington, D.C., and a BioMusic member, applauds the project's efforts to tout the marvels of birdsongs as markers of biodiversity. However, he turns almost stern at the question of whether those sounds are really songs dressed up in feathers.
"Any analogy to human music is not interesting to me," Morton says. "It doesn't explain anything about how the world is, except how humans want to perceive it. Good on 'em, but I want to understand animals."
From a bird's perspective, he argues, song is either "territorial defense or mate attraction, but in both cases it's very-long-distance communication." His 1992 book Animal Talk (Random House) expounds the idea that vocal traditions constitute an avian broadcasting network, letting birds minimize the arduous work of flying about during interactions.
"That's where I think it differs from human music," he says. "Human music isn't particularly distance related."
Entomologist Thomas Eisner of Cornell University likewise draws a distinction between enjoying animal sounds and saying that animals make music.
He remembers Payne bringing him the first recording of humpback whale sounds. "He insisted that we both have a glass of wine before we listened to it," Eisner recalls. "We went to the studio, we put on earphones, and I was sent into outer space."
As an accomplished keyboard player, Eisner says, "If a whale calls me up tomorrow and wants to do an evening of sonatas, I would be the first to volunteer."
Do the whales, however, perceive their sounds as sweet music? "It's an untestable question in scientific terms," he says. "The sense of inner tranquility that I personally get out of listening to the Goldberg Variations I can't test for. I can't even test for it in another human being."
Nonetheless, lobster specialist Jelle Atema of Boston University, who has played flute to Eisner's accompaniment, acknowledges some similarities between human music and animal utterances. "Birds, too, learn their songs and use them to be known and attractive in their social environment," Atema explains. "Males sing. Other males hate them for it and try to sing louder, better, longer to impress the other sex.
"I bet that the effects of all these vocalizations are measurable in hormonal responses that alter the behavior of the listener," Atema says. "And here we may be similar to animals. Galina Vishnevskaya need only sing one note, and she pierces my heart."
Psychologist Carol Krumhansl of Cornell University suggests looking for similarities in perceptions of sound sequences. Her work with music, such as the strings of syllables known as yoiks in Finland, has suggested regularities in the way people learn what to expect next in a melody. She raises the question of whether other species have similar expectations.
In the end, speculating about animal sounds and their effects may tell us mostly about ourselves, says Atema. "All we can do scientifically is to measure our noises, catalog them, analyze their components and structure, and then do the same for animal noises," he says. "'Splitters' will then decide that humans are demonstrably different from animals and thus animals do not have music. 'Lumpers' will see many similarities and conclude from the same data that we all have a lot of music in common."
In all the theorizing over the nature of music, Baptista urges listeners to remember the plight of the musicians. A quail species that Beethoven, Schubert, and Haydn all echoed in their compositions has disappeared in parts of Europe, he laments. The Soccorro mockingbirds, which sing in counterpoint, are losing habitat to sheep.
Beyond all the acoustical analysis, Baptista says, "part of the magic of a bird's song is found in the miracle of the bird itself."
From Science News, Vol. 157, No. 16, April 15, 2000, p. 252.
Fuente:
http://www.sciencenews.org/articles/20000415/bob11.asp
martes, 30 de octubre de 2007
Just Duet
Just Duet
Biologists puzzle over birds' ensemble vocalizations
Susan Milius
As the morning mists rose on the slopes of Ecuador's Pasochoa volcano, the burbling of plain-tailed wrens came through the bamboo thickets. Two researchers started their standard procedure of catching wrens, banding them, and letting them go. Soon, however, they were startled when a small cluster of wrens settled into a bush and began singing together. It turned out to be "one of the most complex singing performances yet described in a nonhuman animal," says Nigel Mann.
a6940_1740.jpg
CHORUS LINES. The song of the plain-tailed wren of Ecuador sounds like one continuous bubbling tone. However, it comes from two birds and often more. In the jagged sonogram trace (bottom), males sing two kinds of sections (under blue bars) and females fill in gaps with two kinds of phrases (under red bars). Double bars represent two same-sex singers.
Mann/Biology Letters
Mann, of the State University of New York at Oneonta, and a colleague had gone to Pasochoa in the summer of 2002 as part of a team that was surveying of the 28-or-so species of the bird genus Thryothorus. That genus is famous for musical duets, in which a male and a female alternate phrases, sometimes so rapidly that it sounds like one song. Ecuador's plain-tailed wrens (Thryothorus euophrys), relatives of North America's Carolina wren, make a rhythmic, bubbling song together.
Most other wrens in this genus pair off and fiercely defend a territory. "If [four wrens] actually got within a few feet of each other, they'd be fighting," says Mann. That's why he and Kimberly A. Dingess of Indiana University at Bloomington were so surprised to find several plain-tailed wrens sharing a bush. "It took a few hours of wandering around for us to realize we had a group-living species," Mann says.
This social oddity has musical consequences. Often, three or more birds sing—males, then females, then males, and so on—to produce what sounds like a single melody.
"It's quite difficult to work out what's Charlie's contribution, what's Mary's," Mann says.
Yet the scientists did work out the score. At rare moments in the several weeks of observation, Mann or Dingess picked up clues to which bird was singing when one singer perched closer to the microphone than the rest of the chorus did.
From these hard-won moments, the researchers realized that songs typically repeat four phrases: ABCDABCD.... Only males sing the As and Cs, and only females sing Bs and Ds. Each singer knows 25-to-30 variations on each of its two possible parts, and for each variation of A, a particular variation of B usually follows, as do particular Ds after Cs.
When more than two birds strike up a tune, they double up on the parts so precisely that if one bird stops singing, the tune keeps going. The males sing the same variation of A with precise timing, followed by the females chorusing the same version of B, then back to the males for the same C, and so on. The parts shift back and forth at least twice a second. For samples of sound files of duets, click here.
It's the first four-part, synchronized chorus with alternating parts recorded outside human music, Mann, Dingess, and Peter J.B. Slater of the University of St. Andrews in Scotland report in the March 22 Biology Letters. And when one considers the split-second alternation, the birds' singing surpasses human vocal virtuosity.
That's the latest, most extreme example of duetting birds, a phenomenon that has fascinated birders for decades and inspired its own chorus of theorizing about what might drive such displays. Warning off rivals? Foiling flirtations? Checking musical passwords? In the past few years, field biologists have applied modern ideas about evolution to begin new tests of why duetters do it.
Singing double
Honks, squeaks, and melodic syllables can all be scored into avian duets. In at least 222 bird species worldwide, or about 3 percent of those known, two or more individuals routinely coordinate their vocalizations.
Duetting shows up in a range of bird families and takes many forms, says Michelle Hall of the Australian National University in Canberra. Although members of a mated pair typically alternate as they sing their parts, duos within some species sing in unison. In a few cases, two males vocalize together, or several birds form an ensemble, as among the plain-tailed wrens.
An ornithological sorrow of life in northern temperate zones is the scarcity of duetting birds. The few nontropical birds that perform together generally do simple numbers.
Ornithologists have described male and female Canada geese alternating honks. And Lauryn Benedict of the University of California, Berkeley is studying a duet of California towhees where male and females produce simultaneous, near-identical, squeal-like vocalizations that are used only in duets and never alone.
Most birds that duet—and the most interesting vocal interactions—come from somewhere other than northern temperate zones.
Among magpie-larks, which Hall studied during the 1990s, males and females sing solo as well as together. Common in Australian suburbs, the long-legged, black-and-white birds "can sound a little raucous," says Hall. Either sex can initiate a duet, typically starting to repeat one of nine musical motifs, such as "peewee," with a gap of a third to a half second between repetitions. On occasion, the mate inserts another motif in the gaps to make, for example, a "peewee o-wit peewee o-wit peewee" duet.
Male eastern whipbirds in Australia start a duet with a whistle and a sound like that of a cracking whip, and females chime in with several notes. Up and down Australia's east coast, males sounded remarkably similar, but females had regional variations, report Amy Rogers of the University of Melbourne and Daniel Mennill of the University of Windsor in Ontario in the January Journal of Avian Biology.
In one of the rare male-male duets, two long-tailed manakins advertise the location of a courtship perch by simultaneously singing "Toledo."
Male-manakin duos with the tightest coordination get the most visitors, report Jill Trainer of the University of Northern Iowa and her colleagues. However, only the dominant male of a singing pair does any mating. The second manakin can spend up to 10 years with no apparent reward but his increasing skill in singing along.
Why, oh why?
Over several decades, scientists have offered at least a dozen explanations for the purpose of avian duets. The theories have focused on the forest, the pair, or conflicts of interest between individual birds.
The abundance of duetting in the tropics inspired some of the early explanations. Scientists in the 1970s noted that dense tropical vegetation would make sound especially important for mates identifying each other or keeping in contact. Recently, theorists have suggested that tropical birds duet to stay in sync reproductively, despite limited seasonal cues such as changes in day length.
Other scientists have stressed the partnership. For example, in the 1980s, the "coyness hypothesis" proposed that birds that consummated their pairing only after the arduous job of learning to duet would have a stronger bond that would discourage extra-pair adventuring.
Yet other theorists have suggested that duetting enables a bird to judge its mate's commitment to the partnership. Discouraging interlopers has been a popular theme, both in duetting to defend a territory and duetting to drive away a potential mate stealer.
Several current duet researchers trace their interest in the field to 1996 papers by Rachel Levin, now of Pomona College in Claremont, Calif. Her work challenged the idea that achieving coordinated singing is a difficult task.
Levin studied Panama's bay wrens, which duet with rapid-fire, his-her alternation. When she kidnapped the mates of 10 bay wrens, the left-behind bird found a new mate and managed immediately to duet almost as well with the new partner as it had with the old.
Too often, these earlier theories treated a duet as a single, cooperative behavior performed for mutual advantage, Levin suggested. Because evolutionary forces act on individuals, Levin urged her colleagues to scrutinize the interests of individuals instead of happy pairs.
Levin's work "reignited the excitement about duets," says Mennill, who was inspired to take up the study of duetting in another tropical wren.
She's/he's mine
The current generation of duetting studies often compares his-and-her agendas. One possible agenda is the male's clear interest in fathering the female's chicks. He may be chiming in to the female's song as a musical claim to paternity. If so, Hall says, then a male should duet more when his partner is fertile than when she's not.
That idea didn't hold up in magpie-larks. Hall found that a female tends to sing less when fertile and that a male is less likely to join in when his singing partner is fertile than when she's not.
a6940_239.jpg
TROPICAL TUNES. Males and females of many tropical Thryothorus wren species, such as the buff-breasted wren, trade parts back and forth so fast that they sound like one song. Sonogram traces 3.5 seconds of a wren duet, with the male's part in purple.
Gill
Buff-breasted wrens (Thryothorus leucotis) in Panama do something similar, says Sharon A. Gill, now at Princeton University. Males go "wop," and at times, females smoothly interpose "weooh."
Gill calculated females' fertile periods by keeping track of when they laid eggs. The mates started duets less frequently during these times than when the females weren't fertile, Gill reported in the April 2005 Behavioral Ecology and Sociobiology.
Males didn't seem that concerned about paternity in general, Gill says. She didn't find them sticking extra close to mates during fertile times. Nevertheless, only one of the 31 broods that she analyzed showed evidence of mixed parentage.
Even if duetting doesn't guard paternity, either partner might have an agenda "to defend their partnership," as Gill puts it. For example, consider the warbling antbirds in the Amazon (Hypocnemis cantator). Males sing solos, and, at times, females add girls-only song elements, report Nathalie Seddon and Joseph Tobias, both of the University of Oxford in England.
When the researchers played songs recorded from other warbling antbirds, both males and females were more likely to approach the speaker and to sing in response to same-sex solos than to male-female duets. When antbird couples hear recorded solos of a female, the resident male usually begins to sing. But then the resident female typically jumps in to duet sooner and more often than she does after recorded duets or male solos. That female is duetting to discourage same-sex interlopers, the researchers suggest in the January/February Behavioral Ecology.
African birds called tropical boubous (Laniarius aethiopicus) also show signs of mate guarding, but with a twist, Ulmar Grafe and Johannes Bitz of the University of Würzburg in Germany reported in 2004. When they played recorded male solos to pairs of birds, the female joined in to sing along. Then, in half of the six pairs studied, the female's mate started overlapping the notes in the recorded male solo. Grafe and Bitz interpreted this as a male jamming the signal from a too-enticing male intruder.
My land
Territory, as well as mates, might be worth duetting for. As many of the tropical duetters do, rufous-and-white wrens (Thryothorus rufalbus) defend their turf year-round. Their duets are "fluty, haunting-sounding," says Mennill, in contrast to the more-staccato bursts of other tropical wrens. In 70 percent of the rufous-and-white wrens' duets, the females join a male song, rather than the male picking up on a female's vocalization, Mennill reported in the January 2005 Auk.
The researcher moved around a pair of speakers, one broadcasting a male part in a duet and the other featuring the female, in an action mimicking that of a pair of wrens trespassing on various territories. The rightful territory owners approached the speakers with extra bursts of their own solo and duet songs. They wagged their tails and chattered harshly at the speakers, as they do when chasing off real invaders, Mennill reports in the January Animal Behaviour.
Other studies in different species have pointed out that duetting birds often sing loudly from easy-to-see perches, just as solo territorial songsters do. Soloists and duetters both match bits of their songs with those of potential intruders, a one-upmanship contest (SN: 12/18&25/04, p. 397; Available to subscribers at http://www.sciencenews.org/articles/20041218/bob10.asp).
Grafe and Bitz have even proposed that boubous sing a particular kind of duet to advertise to the neighborhood that they've trounced a rival. The scientists have broadcast songs to simulate an invading pair of boubous and then compared the duets of resident birds that fled from the invasion with duets of birds that held their ground. After the confrontation, the steadfast pairs used a particular configuration of male-and-female notes in a duet that fleeing birds didn't use, the researchers reported in 2004.
The fury of territory defense led two researchers in 2004 to propose another function of duetting: distinguishing a fellow defender from an enemy. Black-bellied wrens (Thryothorus fasciatoventris) fuss and sing when researchers broadcast songs to mimic intruders, says David Logue of the University of Lethbridge in Alberta. He's researching what he calls duet codes, rules saying that a male's musical motif X goes with a female's motif Y. Females "always blast out the right answer," says Logue.
He and David Gammon of St. Edward's University in Austin, Texas, suggested in 2004 that duetting offers a way for black-bellied wren females to make sure that their mates don't attack them by mistake. The dense forests where these birds live distort sounds such as the "here I am" calls that other species use, says Logue. The wrens need an especially strong password system to tell friend from foe, he says.
Hall recounts anecdotes of attacks on intruders by cooperating birds. Purple-crowned fairy wrens, for example, spend much of their time near each other. "If one hops half-a-meter away, the other hops too," she says. And when they hear recorded songs in stereo, they both fly to chasten one speaker and then move together to the second. Hall says that she hopes someone will explore how widespread such defensive coordination might be among duetters.
All the ideas about the function of duets need more testing, she adds.
As bird duets start to make sense, maybe they'll shed light on other duetting species. Birds duet. Bugs duet. Even some primates do it.
All Together Now . . .
Employing terms and phrases such as "Toledo," "wop," "weooh," and "peewee o-wit peewee o-wit peewee" bird duet researchers can be quite creative in describing the sound recordings used in their work. Since there is no substitute for the original, however, we thought we'd supply a sampling of the actual sound files, along with tips from the scientists about what to listen for. For ease of reference, we have provided a link here, which will open the main article, "Just Duet," in a separate window.
From Nigel Mann:
Four-part chorus in plain-tailed wrens (Thryothorus euophrys).
a6940_340.jpg
p-t fig, 2nd.wav - This is a wren chorus of the type shown in the sonogram at right. Males sing the first and third elements (under blue bars) in each segment, and females interpose the second and fourth elements (under red bars). Double bars mean two birds are singing in unison (210 KB WAV file).
p-t long song.wav - This is a longer recording of the same species (1 MB WAV file).
From Lauryn Benedict:
Male-female duet in the California towhee, a rare temperate zone example of this behavior.
a6940_4192.jpg
Photo by Neil Losin
CALT song (161) 4-14-05.wav - This is an example of a typical male solo song (324 KB WAV file).
CALT duet (27&42) 6-28-04.wav - This duet of a male and female incorporates elements which males rarely sing alone. Females never sing other song types at all (453 WAV file).
From Daniel Mennill and Amy Rogers:
Eastern whipbird (Psophodes olivaceus) males start a duet with a whistle and a sound like a cracking whip.
The researchers include sonograms and sound files showing the regional variation found in female contributions to duets on their Web site at: http://web2.uwindsor.ca/courses/biology/dmennill/EAWH.html.
From Daniel Mennill:
Long-tailed manakins represent a rare example of a male-male duet.
Daniel Mennill's Web site includes a page with the "toledo" duet by two courting males, as well as other phrases used in the courting display at: http://web2.uwindsor.ca/courses/biology/
dmennill/CostaRica/LTMA/CRLTMA.html.
From Sharon Gill:
Buff-breasted wren (Thryothorus leucotis) males and females trade parts back and forth within seconds.
a6940_5975.jpg
Photo by E.D. Alfson
Male-initiated duet.aif - An example of a duet initiated by the male (338 KB AIF file).
Female-initiated duet.aif - A duet started by the female of a mated pair (515 KB AIF file).
From Daniel Mennill:
Rufous-and-white wrens (Thryothorus rufalbus) defend their territory year-round.
A variety of solos and duets, which he describes as "fluty, [and] haunting-sounding" can be found on Dan Mennill's Web site at: http://web2.uwindsor.ca/courses/biology/
dmennill/CostaRica/RWWR/CRRWWR.html.
From David Logue:
An example of a possible password code employed by black-bellied wrens (Thryothorus fasciatoventris).
To understand the duet code, Logue says, "Listen to the duet first, then the male and female songs that make it up, then the duet again. You can hear how in the duet, the female is responding to the male changing song type (1-2-1) by changing the song types she's using as responses (also 1-2-1)."
Duet.wav – The full duet (438 KB WAV file).
Male song 1.wav – Male song type 1 (87 KB WAV file).
Female song 1.wav – Female song type 1 (84 KB WAV file).
Male song 2.wav – Male song type 2 (82 KB WAV file).
Female song 2.wav – Female song type 2 (72 KB WAV file).
Fuente:
http://www.sciencenews.org/articles/20060128/bob9.asp
From Science News, Vol. 169, No. 4, Jan. 28, 2006, p. 58.
Biologists puzzle over birds' ensemble vocalizations
Susan Milius
As the morning mists rose on the slopes of Ecuador's Pasochoa volcano, the burbling of plain-tailed wrens came through the bamboo thickets. Two researchers started their standard procedure of catching wrens, banding them, and letting them go. Soon, however, they were startled when a small cluster of wrens settled into a bush and began singing together. It turned out to be "one of the most complex singing performances yet described in a nonhuman animal," says Nigel Mann.
a6940_1740.jpg
CHORUS LINES. The song of the plain-tailed wren of Ecuador sounds like one continuous bubbling tone. However, it comes from two birds and often more. In the jagged sonogram trace (bottom), males sing two kinds of sections (under blue bars) and females fill in gaps with two kinds of phrases (under red bars). Double bars represent two same-sex singers.
Mann/Biology Letters
Mann, of the State University of New York at Oneonta, and a colleague had gone to Pasochoa in the summer of 2002 as part of a team that was surveying of the 28-or-so species of the bird genus Thryothorus. That genus is famous for musical duets, in which a male and a female alternate phrases, sometimes so rapidly that it sounds like one song. Ecuador's plain-tailed wrens (Thryothorus euophrys), relatives of North America's Carolina wren, make a rhythmic, bubbling song together.
Most other wrens in this genus pair off and fiercely defend a territory. "If [four wrens] actually got within a few feet of each other, they'd be fighting," says Mann. That's why he and Kimberly A. Dingess of Indiana University at Bloomington were so surprised to find several plain-tailed wrens sharing a bush. "It took a few hours of wandering around for us to realize we had a group-living species," Mann says.
This social oddity has musical consequences. Often, three or more birds sing—males, then females, then males, and so on—to produce what sounds like a single melody.
"It's quite difficult to work out what's Charlie's contribution, what's Mary's," Mann says.
Yet the scientists did work out the score. At rare moments in the several weeks of observation, Mann or Dingess picked up clues to which bird was singing when one singer perched closer to the microphone than the rest of the chorus did.
From these hard-won moments, the researchers realized that songs typically repeat four phrases: ABCDABCD.... Only males sing the As and Cs, and only females sing Bs and Ds. Each singer knows 25-to-30 variations on each of its two possible parts, and for each variation of A, a particular variation of B usually follows, as do particular Ds after Cs.
When more than two birds strike up a tune, they double up on the parts so precisely that if one bird stops singing, the tune keeps going. The males sing the same variation of A with precise timing, followed by the females chorusing the same version of B, then back to the males for the same C, and so on. The parts shift back and forth at least twice a second. For samples of sound files of duets, click here.
It's the first four-part, synchronized chorus with alternating parts recorded outside human music, Mann, Dingess, and Peter J.B. Slater of the University of St. Andrews in Scotland report in the March 22 Biology Letters. And when one considers the split-second alternation, the birds' singing surpasses human vocal virtuosity.
That's the latest, most extreme example of duetting birds, a phenomenon that has fascinated birders for decades and inspired its own chorus of theorizing about what might drive such displays. Warning off rivals? Foiling flirtations? Checking musical passwords? In the past few years, field biologists have applied modern ideas about evolution to begin new tests of why duetters do it.
Singing double
Honks, squeaks, and melodic syllables can all be scored into avian duets. In at least 222 bird species worldwide, or about 3 percent of those known, two or more individuals routinely coordinate their vocalizations.
Duetting shows up in a range of bird families and takes many forms, says Michelle Hall of the Australian National University in Canberra. Although members of a mated pair typically alternate as they sing their parts, duos within some species sing in unison. In a few cases, two males vocalize together, or several birds form an ensemble, as among the plain-tailed wrens.
An ornithological sorrow of life in northern temperate zones is the scarcity of duetting birds. The few nontropical birds that perform together generally do simple numbers.
Ornithologists have described male and female Canada geese alternating honks. And Lauryn Benedict of the University of California, Berkeley is studying a duet of California towhees where male and females produce simultaneous, near-identical, squeal-like vocalizations that are used only in duets and never alone.
Most birds that duet—and the most interesting vocal interactions—come from somewhere other than northern temperate zones.
Among magpie-larks, which Hall studied during the 1990s, males and females sing solo as well as together. Common in Australian suburbs, the long-legged, black-and-white birds "can sound a little raucous," says Hall. Either sex can initiate a duet, typically starting to repeat one of nine musical motifs, such as "peewee," with a gap of a third to a half second between repetitions. On occasion, the mate inserts another motif in the gaps to make, for example, a "peewee o-wit peewee o-wit peewee" duet.
Male eastern whipbirds in Australia start a duet with a whistle and a sound like that of a cracking whip, and females chime in with several notes. Up and down Australia's east coast, males sounded remarkably similar, but females had regional variations, report Amy Rogers of the University of Melbourne and Daniel Mennill of the University of Windsor in Ontario in the January Journal of Avian Biology.
In one of the rare male-male duets, two long-tailed manakins advertise the location of a courtship perch by simultaneously singing "Toledo."
Male-manakin duos with the tightest coordination get the most visitors, report Jill Trainer of the University of Northern Iowa and her colleagues. However, only the dominant male of a singing pair does any mating. The second manakin can spend up to 10 years with no apparent reward but his increasing skill in singing along.
Why, oh why?
Over several decades, scientists have offered at least a dozen explanations for the purpose of avian duets. The theories have focused on the forest, the pair, or conflicts of interest between individual birds.
The abundance of duetting in the tropics inspired some of the early explanations. Scientists in the 1970s noted that dense tropical vegetation would make sound especially important for mates identifying each other or keeping in contact. Recently, theorists have suggested that tropical birds duet to stay in sync reproductively, despite limited seasonal cues such as changes in day length.
Other scientists have stressed the partnership. For example, in the 1980s, the "coyness hypothesis" proposed that birds that consummated their pairing only after the arduous job of learning to duet would have a stronger bond that would discourage extra-pair adventuring.
Yet other theorists have suggested that duetting enables a bird to judge its mate's commitment to the partnership. Discouraging interlopers has been a popular theme, both in duetting to defend a territory and duetting to drive away a potential mate stealer.
Several current duet researchers trace their interest in the field to 1996 papers by Rachel Levin, now of Pomona College in Claremont, Calif. Her work challenged the idea that achieving coordinated singing is a difficult task.
Levin studied Panama's bay wrens, which duet with rapid-fire, his-her alternation. When she kidnapped the mates of 10 bay wrens, the left-behind bird found a new mate and managed immediately to duet almost as well with the new partner as it had with the old.
Too often, these earlier theories treated a duet as a single, cooperative behavior performed for mutual advantage, Levin suggested. Because evolutionary forces act on individuals, Levin urged her colleagues to scrutinize the interests of individuals instead of happy pairs.
Levin's work "reignited the excitement about duets," says Mennill, who was inspired to take up the study of duetting in another tropical wren.
She's/he's mine
The current generation of duetting studies often compares his-and-her agendas. One possible agenda is the male's clear interest in fathering the female's chicks. He may be chiming in to the female's song as a musical claim to paternity. If so, Hall says, then a male should duet more when his partner is fertile than when she's not.
That idea didn't hold up in magpie-larks. Hall found that a female tends to sing less when fertile and that a male is less likely to join in when his singing partner is fertile than when she's not.
a6940_239.jpg
TROPICAL TUNES. Males and females of many tropical Thryothorus wren species, such as the buff-breasted wren, trade parts back and forth so fast that they sound like one song. Sonogram traces 3.5 seconds of a wren duet, with the male's part in purple.
Gill
Buff-breasted wrens (Thryothorus leucotis) in Panama do something similar, says Sharon A. Gill, now at Princeton University. Males go "wop," and at times, females smoothly interpose "weooh."
Gill calculated females' fertile periods by keeping track of when they laid eggs. The mates started duets less frequently during these times than when the females weren't fertile, Gill reported in the April 2005 Behavioral Ecology and Sociobiology.
Males didn't seem that concerned about paternity in general, Gill says. She didn't find them sticking extra close to mates during fertile times. Nevertheless, only one of the 31 broods that she analyzed showed evidence of mixed parentage.
Even if duetting doesn't guard paternity, either partner might have an agenda "to defend their partnership," as Gill puts it. For example, consider the warbling antbirds in the Amazon (Hypocnemis cantator). Males sing solos, and, at times, females add girls-only song elements, report Nathalie Seddon and Joseph Tobias, both of the University of Oxford in England.
When the researchers played songs recorded from other warbling antbirds, both males and females were more likely to approach the speaker and to sing in response to same-sex solos than to male-female duets. When antbird couples hear recorded solos of a female, the resident male usually begins to sing. But then the resident female typically jumps in to duet sooner and more often than she does after recorded duets or male solos. That female is duetting to discourage same-sex interlopers, the researchers suggest in the January/February Behavioral Ecology.
African birds called tropical boubous (Laniarius aethiopicus) also show signs of mate guarding, but with a twist, Ulmar Grafe and Johannes Bitz of the University of Würzburg in Germany reported in 2004. When they played recorded male solos to pairs of birds, the female joined in to sing along. Then, in half of the six pairs studied, the female's mate started overlapping the notes in the recorded male solo. Grafe and Bitz interpreted this as a male jamming the signal from a too-enticing male intruder.
My land
Territory, as well as mates, might be worth duetting for. As many of the tropical duetters do, rufous-and-white wrens (Thryothorus rufalbus) defend their turf year-round. Their duets are "fluty, haunting-sounding," says Mennill, in contrast to the more-staccato bursts of other tropical wrens. In 70 percent of the rufous-and-white wrens' duets, the females join a male song, rather than the male picking up on a female's vocalization, Mennill reported in the January 2005 Auk.
The researcher moved around a pair of speakers, one broadcasting a male part in a duet and the other featuring the female, in an action mimicking that of a pair of wrens trespassing on various territories. The rightful territory owners approached the speakers with extra bursts of their own solo and duet songs. They wagged their tails and chattered harshly at the speakers, as they do when chasing off real invaders, Mennill reports in the January Animal Behaviour.
Other studies in different species have pointed out that duetting birds often sing loudly from easy-to-see perches, just as solo territorial songsters do. Soloists and duetters both match bits of their songs with those of potential intruders, a one-upmanship contest (SN: 12/18&25/04, p. 397; Available to subscribers at http://www.sciencenews.org/articles/20041218/bob10.asp).
Grafe and Bitz have even proposed that boubous sing a particular kind of duet to advertise to the neighborhood that they've trounced a rival. The scientists have broadcast songs to simulate an invading pair of boubous and then compared the duets of resident birds that fled from the invasion with duets of birds that held their ground. After the confrontation, the steadfast pairs used a particular configuration of male-and-female notes in a duet that fleeing birds didn't use, the researchers reported in 2004.
The fury of territory defense led two researchers in 2004 to propose another function of duetting: distinguishing a fellow defender from an enemy. Black-bellied wrens (Thryothorus fasciatoventris) fuss and sing when researchers broadcast songs to mimic intruders, says David Logue of the University of Lethbridge in Alberta. He's researching what he calls duet codes, rules saying that a male's musical motif X goes with a female's motif Y. Females "always blast out the right answer," says Logue.
He and David Gammon of St. Edward's University in Austin, Texas, suggested in 2004 that duetting offers a way for black-bellied wren females to make sure that their mates don't attack them by mistake. The dense forests where these birds live distort sounds such as the "here I am" calls that other species use, says Logue. The wrens need an especially strong password system to tell friend from foe, he says.
Hall recounts anecdotes of attacks on intruders by cooperating birds. Purple-crowned fairy wrens, for example, spend much of their time near each other. "If one hops half-a-meter away, the other hops too," she says. And when they hear recorded songs in stereo, they both fly to chasten one speaker and then move together to the second. Hall says that she hopes someone will explore how widespread such defensive coordination might be among duetters.
All the ideas about the function of duets need more testing, she adds.
As bird duets start to make sense, maybe they'll shed light on other duetting species. Birds duet. Bugs duet. Even some primates do it.
All Together Now . . .
Employing terms and phrases such as "Toledo," "wop," "weooh," and "peewee o-wit peewee o-wit peewee" bird duet researchers can be quite creative in describing the sound recordings used in their work. Since there is no substitute for the original, however, we thought we'd supply a sampling of the actual sound files, along with tips from the scientists about what to listen for. For ease of reference, we have provided a link here, which will open the main article, "Just Duet," in a separate window.
From Nigel Mann:
Four-part chorus in plain-tailed wrens (Thryothorus euophrys).
a6940_340.jpg
p-t fig, 2nd.wav - This is a wren chorus of the type shown in the sonogram at right. Males sing the first and third elements (under blue bars) in each segment, and females interpose the second and fourth elements (under red bars). Double bars mean two birds are singing in unison (210 KB WAV file).
p-t long song.wav - This is a longer recording of the same species (1 MB WAV file).
From Lauryn Benedict:
Male-female duet in the California towhee, a rare temperate zone example of this behavior.
a6940_4192.jpg
Photo by Neil Losin
CALT song (161) 4-14-05.wav - This is an example of a typical male solo song (324 KB WAV file).
CALT duet (27&42) 6-28-04.wav - This duet of a male and female incorporates elements which males rarely sing alone. Females never sing other song types at all (453 WAV file).
From Daniel Mennill and Amy Rogers:
Eastern whipbird (Psophodes olivaceus) males start a duet with a whistle and a sound like a cracking whip.
The researchers include sonograms and sound files showing the regional variation found in female contributions to duets on their Web site at: http://web2.uwindsor.ca/courses/biology/dmennill/EAWH.html.
From Daniel Mennill:
Long-tailed manakins represent a rare example of a male-male duet.
Daniel Mennill's Web site includes a page with the "toledo" duet by two courting males, as well as other phrases used in the courting display at: http://web2.uwindsor.ca/courses/biology/
dmennill/CostaRica/LTMA/CRLTMA.html.
From Sharon Gill:
Buff-breasted wren (Thryothorus leucotis) males and females trade parts back and forth within seconds.
a6940_5975.jpg
Photo by E.D. Alfson
Male-initiated duet.aif - An example of a duet initiated by the male (338 KB AIF file).
Female-initiated duet.aif - A duet started by the female of a mated pair (515 KB AIF file).
From Daniel Mennill:
Rufous-and-white wrens (Thryothorus rufalbus) defend their territory year-round.
A variety of solos and duets, which he describes as "fluty, [and] haunting-sounding" can be found on Dan Mennill's Web site at: http://web2.uwindsor.ca/courses/biology/
dmennill/CostaRica/RWWR/CRRWWR.html.
From David Logue:
An example of a possible password code employed by black-bellied wrens (Thryothorus fasciatoventris).
To understand the duet code, Logue says, "Listen to the duet first, then the male and female songs that make it up, then the duet again. You can hear how in the duet, the female is responding to the male changing song type (1-2-1) by changing the song types she's using as responses (also 1-2-1)."
Duet.wav – The full duet (438 KB WAV file).
Male song 1.wav – Male song type 1 (87 KB WAV file).
Female song 1.wav – Female song type 1 (84 KB WAV file).
Male song 2.wav – Male song type 2 (82 KB WAV file).
Female song 2.wav – Female song type 2 (72 KB WAV file).
Fuente:
http://www.sciencenews.org/articles/20060128/bob9.asp
From Science News, Vol. 169, No. 4, Jan. 28, 2006, p. 58.
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