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Those Who Sing Together, Mate Together
By Katharina Kramer
Some animals are better musicians than first thought. Far from belting out random notes, some species sing complicated duets. Researchers believe the concerts bring mates closer together.
The first birds that sang on that October morning, 3,500 meters (11,480 feet) up in the Ecuadorian Andes, came from a tape player. But just minutes later, ornithologist Nigel Mann was surrounded by the real thing -- reddish-brown wrens had fluttered onto the branches around him and had formed a boisterous choir.
In a furious presto, the agitated birds sang four phrases with the male and female voices breathlessly alternating parts. The pitch and tempo were so precise that it sounded as if only a single bird were singing. With their song, the winged locals were trying to spook the fictitious, unwanted visitors the birdwatcher had brought on tape.
The researcher could hardly believe his luck: "It was truly the most complex group melody known in the animal world," Mann says. He then stunned his colleagues with an essay describing the perfection of the plain-tailed wrens' duet. He knew the bird world would be all aflutter -- more and more scientists are taking an interest in coordinated animal song.
According to the most recent research, only birds, monkeys and whales are capable of concert-like performances. And only 3 percent of all birds -- or just 200 species -- sing in duet. Only a handful are known to perform in choirs and no other bird has achieved the perfect synchronization of the plain-tailed wren.
The musical talent of monkeys
But monkeys have musical talent too -- 12 percent of all species sing in duet. The most beautiful ape songs are created in the throats of the gibbon, which often perform whistling concerts. The musical talent of whales was often passed over by researchers, who in recent years began noticing hints of coordinated tones.
"The motivation behind researching the songs of animals is always the age-old dream of deciphering their language," says French bioacoustics specialist Michel André, who studies the utterances of sperm whales at the Polytechnic Institute in Barcelona. But the main goal of researching animal concerts is to discover their social function, adds ornithologist Mann, who teaches at New York State University.
Conspicuously, nearly all birds that sing in pairs live in the tropics. In moderate climes, only male birds are responsible for guarding the territory and attracting a mate. In the tropics, however, many females use song to defend their space as well as synchronize mating behavior with partners. In a tropical environment without seasons, there's no spring to roust the birds and the bees. Duets, it seems, stimulate sexual hormones.
But above all, singing together appears to strengthen the bond between pairs and groups -- and this is especially important in the tropics. The plain-tailed wren lives in a group year-round. Males and females in other species in those regions also spend the entire year -- or even an entire lifetime -- with each other. In moderate climes, most avian relationships just last the summer.
A broad repertoire
This lengthy togetherness gives tropical birds the time to practice complex melodies -- something demanded by the song of the plain-tailed wren. The birds alternate parts, synchronize and cover four stanzas per song. Moreover, each individual animal has a repertoire of 20 stanzas. The first bird that opens his beak determines the structure of the song for the subsequent singers. The harmonious mass singing is apparently to discourage outsiders and demonstrate team spirit.
The role of singing within the social structure of monkeys is more apparent than for birds. "The evolution of song and duets is related to the evolution of monogamy in primates," says Thomas Geissmann of the Anthropological Institute at the University of Zurich. Many species of singing monkey are indeed monogamous including the gibbons of Southeast Asia, the indris of Madagascar, the titi monkeys in South America and the wide-eyed, nocturnal spectral tarsiers on the Indonesian island of Sulawesi.
Bolivian gray titi monkeys form especially intimate couples. "Males and females do practically everything together," reports anthropologist Kimberly Dingess from Indiana University, who observes the animals in the wild. "This is equally true for foraging, child rearing and marking their territory." Couples often strike a romantic pose, intertwining their long tails while clinging tightly to each other on a branch and singing in unison.
Their melody is primarily barking, screaming and panting, and both males and females rely on the same repertoire. In contrast to birds, monkeys don't learn by imitation. Bolivian gray titi monkeys, like all singing monkeys, are natural talents. The males begin each song with a loud moaning. The female then barks verse A while the male sings verse B. Both pant during a brief intermezzo until the female returns to song with verse B. The male then chimes in, repeating verse A. The performance lasts for about three minutes and is held regularly. Often, the monkey tune can be heard at dawn on the edge of a pair's neighborhood. "The couple wants to make it clear: We are still here and are protecting our territory," explains Dingess.
Those who sing together, stay together
The master of the monkey duet is the Siamang gibbon. Both sexes possess the same repertoire but newlyweds must first synchronize their singing. And this brings them closer together: "Leaving a partner doesn't appear to be very attractive because the duets of fresh couples are noticeably poor," says gibbon expert Geissmann. And performing poorly in a duet can cost a monkey a partner or territory.
Mann and his colleagues now hope to discover just how close the link is between duets and partnership by studying the approximately 30 species of plain-tailed wrens in Latin America. Initial findings indicate that bird species that breed, forage and protect their territory together, sing better together. However, in species where the sexes have differing roles and males pay little attention to the offspring, duets are rarely harmonic: "More pauses, phrases run into each other, less synchronization," says Mann.
The coordination between sperm whales has yet to be researched in depth but it's apparent that the giant mammals live in especially tight social groups. Every member uses a unique clicking rhythm that it learned sometime after birth. Researchers used to believe the clicks were pure cacophony. But while observing a group of 12 whales near the Canary Islands, acoustics specialist André noticed that the rhythms are all similar to that of the most experienced member. "As the sperm whale ages, its rhythm slows," explains the scientist.
Where's my mate?
The most unhurried rhythm sets the time for the others. This synchronization allows the pod to ascertain the location of all members and change direction in unison -- no easy task since sperm whales spread out over 15 kilometers (9.3 miles) and can dive as deep as 3,000 meters (9,840 feet) while hunting for food. André believes it's likely that the clicks and whines of other whales may be similarly coordinated.
Only one type of animal is known to sing in duet without a complex social structure -- some grasshoppers chirp together in well-ordered alternation. The goal is apparently limited to mating.
But then why do grasshoppers even bother singing? One theory is their excellent camouflage, says zoologist Andreas Stumpner from Göttingen. "If they didn't sing, they probably couldn't see their partner."
Translated from the German by Andrew Bulkeley