Becoming a Tiger: The Education of an Animal Child Read online

  A few animals can learn part of their vocal communication, but this is fairly rare. So far, the ability to learn to produce vocal communication has been found in four orders of mammals and three orders of birds. The mammalian orders are primates (featuring wonderful us), cetaceans (whales and dolphins), pinnipeds (seals, sea lions, and walruses), and bats (for example, the spear-nosed bats of the Caribbean who apparently learn the catchwords of the in-group in order to exclude the out-group from good feeding spots).

  Among birds, vocal learning has been found in the psittaciformes, passerines (or passeriformes), and trochiliformes. Psittaciformes are the parrots, and we all know they can learn novel words and sounds. Passerines are a huge group of birds, sometimes called the songbirds, and they include chickadees, mynahs, and the world’s biggest songbird, the raven. Trochiliformes are the hummingbirds.

  Vocal learning in bats and in hummingbirds is a recent revelation, so it may be that there are other groups of birds or animals out there who learn what to say.

  Why do birds sing so gay?

  Why are birds in these three orders able to learn song? What do they get out of it? Maybe it’s just a case of sexual selection gone wild. If birds are attracted to, mate with, and have more chicks with the best singers, and if they like novelty, then the ability to learn a little would give a bird an edge. Once the brain allows vocal learning, some species might put it to other uses, such as to establish territory or group identity.

  Female great reed warblers prefer a guy who can sing anything in the songbook to those who keep singing the same old tune. Sadly, great reed warblers, both male and female, have a tendency to cheat on their mates. Female reed warblers may cheat with neighbor males if the neighbor sings more songs than their own mate, but if he sings fewer, they don’t bother. Since great reed warblers expand their repertoires as they get older, knowing many songs indicates that the bird in question is a survivor, perhaps because he has a fine set of genes. Indeed, more of the fledglings fathered by the great singers survive to breed the following year.

  What’s this I hear?

  Even species that don’t learn how to make vocalizations must often learn what certain sounds mean, or at least who’s making them. The first such task of the baby animal is learning the sound of its parents’ voices. A baby animal hears not only its mother’s heartbeat in utero, it hears her voice. Mother llamas hum to their babies, and pregnant llamas begin humming a few weeks before giving birth. Chicks in the shell hear their parents’ voices.

  A newborn fur seal pup will answer the call of any female, but by the time it is a few days old, it only answers its mother. Researchers studying a fur seal colony on an island in the Indian Ocean found that the mother doesn’t leave the island to eat until she and her pup know each other’s voice from those of all the other seals in the crowded colony. When a mother returns, she flops inland, calling. The pup calls back, and the two call until they meet. In the months to come, the mother goes to sea and forages for two or three weeks at a time—and comes back to a joyful reunion.

  Brother bird

  Little blue penguin chicks on Tiritiri Matangi Island, New Zealand, are raised in burrows, often with one sibling. If they were temporarily abducted and put in a fake burrow, their little hearts beat faster when they heard their brother’s or sister’s voice, but they remained impassive if they heard a strange penguin chick’s voice. Their hearts also raced at the voices of the chicks from neighboring burrows. Music did not thrill them, nor did the calls of petrels.

  Spectacled parrotlets are small, sociable birds. Although they are enthusiastically monogamous, they spend most days in flocks of up to 25 birds, and roost at night in flocks of up to 150. In the breeding season they nest in cavities, but stay in touch with their group. When all their chicks have fledged, they get together with neighbors who have kids and set up a crèche in a tree where fledglings hang out together. Within the crèches, the young birds are very close to their siblings, and these sibling groups are the main social unit that helps the young birds integrate into the life of the flock.

  Suspecting strongly that birds in the parrot family are just as talented as passerines at recognizing voices, researchers did playback tests with parrotlets in aviaries and determined not only that mates recognize each other’s voices, but that siblings recognize the voices of siblings, even after they have grown up. (Perhaps it pays to stay close to your siblings, researchers suggested, in case you lose your mate—you can fall back on your siblings.)

  How-de-do, neighborinos

  Whether you live in the city, in the country, or on a crowded coral reef, it’s useful to know your neighbors. Bicolor damselfish lead lives that can easily be compared to those of some primates: they live in small, mixed-sex groups, and hold territories on the reefs. Biologists Arthur Myrberg Jr. and Robert Riggio call them “vociferous” and “highly soniferous.” During the spawning season the males each maintain a residence in the colony, containing a nest where females come and lay eggs. The male tends these eggs, fanning fresh water across them and fiercely protecting them. Males on their territory perform diving displays of dips while chirping. This serves to attract females and warn other males that the territory is occupied.

  Myrberg and Riggio taped the chirps of bicolor damselfish at one colony off the Florida coast, played them back, and noted the responses. Males were blasé about the chirps of their nearest neighbors, responding with a mere two-dip display. The chirps of more distant neighbors produced four to six dips, as did playbacks of their own chirps. Presumably they did not recognize their own chirps, just as most people don’t recognize recordings of their voices when they first hear them (and typically reject the suggestion that the squeaky fool on the tape is their sonorous self).

  To explore whether the damselfish weren’t just used to the sounds of their nearest neighbors, but actually knew whose voice was whose, the scientists played the chirps of the neighbors from the wrong territories. Thus a damselfish would hear the familiar chirps of Roy Righthand coming from the territory of Leo Lefthand, or vice versa. This got them horribly upset, and they upped their dipping rate, bicolor damselfish Number Two dipping 14 times when he detected this violation of the established order of things.

  Wolves also listen to their neighbors, using howling as a way to reunite with pack members and to communicate with and learn about other packs. Wolf researchers in northern Minnesota spent many evenings howling at wild wolves. For science. Many of the wolves were radio-collared, so researchers could find out not only whether they howled back, but whether they moved.

  Wolves apparently treat the howls of (skilled) wolf researchers as the howls of wolves unknown to them: loud strangers. If they had a kill, or small pups, they were apt to howl back (“This is our territory—you got a problem with that?”). But if they had no food to protect and no small puppies, they were less likely to howl back. Sometimes they would silently sneak away from the howls. Lone wolves (with no territory) almost never howled back. On several occasions lone females silently headed in the direction of the strange howling, possibly hoping to meet a nice guy. (“SF seeks SM. Should enjoy long walks, big-game hunting. No smokers, humans.”)

  Birdsong

  The basic model of birdsong learning was developed principally with white-crowned sparrows, although it applies to many species. These are bouncy little birds who like to sing from the tops of bushes. The adult males have white crowns, handsomely bordered with black stripes.

  In their youth, they go through a sensitive period, when they hear and remember the sound of white-crowned sparrow songs, probably sung by their father, but also by birds on neighboring territories. They don’t sing yet. When they are a little older they go through a period of subsong—quiet, inexpert song in which they seem to be rehearsing, as if under their breath, all the song types they heard when they were younger. When the males are older, setting up territories and courting females, they loudly and expertly sing just a few chosen song types, in what is called crys
tallized song.

  Song templates

  Most songbirds are not inclined to sing just anything. They have innate templates which give them the general idea of their principal song type. The template hints what a good length for a song might be, and what’s a good range of pitches, and how many phrases would sound nice. “Zebra Finches must learn the details of their song-phrase since only a rough version exists without learning,” writes Richard Zann. But if they are raised by a Bengalese finch foster father, they will learn his song, which will completely “mask” the zebra finch framework.

  A male zebra finch will utter the classic zebra finch Distance Call no matter who raises him, but if the father who raises him isn’t a zebra finch who can model the call for him, it will lack a “noise component” on the end. Females raised by Bengalese finches have essentially normal Distance Calls, if perhaps a little high-pitched.

  Before you criticize zebra finches for having different male and female calls, consider the case of their near relative, the double-barred finch, whose calls are unisex. Zann writes that “strangers probably require several minutes, or possibly hours of behavioural interaction or ‘interrogation’ in order to determine each other’s sex. Certainly, males…have difficulty identifying the sex of strangers in captivity and usually court everyone they encounter until they learn their sex.” That’s got to be awkward.

  It’s not that simple

  Additional research has revealed all kinds of additions, exceptions, and complications to this basic outline, as is usual with real life. Sensitive periods are more flexible than was originally thought. Particularly if the birds haven’t heard anything worth learning, they are able to learn new songs later than usual. Some birds, like canaries and starlings, are “open learners,” who change their songs every year.

  Scientists have also had to amend their assumptions about the experimental procedures they have used. It turns out that most birds learn far better (or only) if they have a live tutor, as opposed to a recording. Researchers like to use recordings because you can ensure that every bird in an experiment hears the exact same thing. But it turns out that birds are not nearly as impressed by canned music as they are by live performances.

  If they can’t have a live tutor, it helps if they can control their learning process. Patrice Adret trained isolated zebra finches to peck a key that turned on a recording of a zebra finch song. The young birds played the tape over and over, and fluttered in front of the loudspeaker while the song played. They learned and sang the song, whereas birds that heard the same songs on the same schedule, but didn’t get to push the buttons, did not learn the songs.

  Subsong and babbling

  Wild zebra finches begin practicing—singing subsong—as early as four weeks old, when they are still with their family. They sing so softly that often the only way you can tell, even if you’re very near, is by their posture. If a young bird could go into its room and close the door, it would.

  Why so quiet? A scornful nineteenth-century auditor wrote of young song sparrows, “I actually laughed aloud at their crude, tuneless, quasi-musical efforts. They were not in good voice and, besides, had not yet fully learned the tunes that are sung in sparrowdom, and could not control their vocal chords. They made many sorry and amusing attempts to chant and trill, but their voices would break and catch in the most remarkable ways, now sliding too high up in the scale, now sliding down too low, and now veering too much to one side, so to speak. One tyro, I observed, sang the first part of a run very well, almost as well, in fact, as an adult musician could have sung it; but when he tried to finish, his voice seemed to fly all to flinders.” The writer then proceeded to a swamp, where he heard adult males singing and exclaimed, “What a contrast between the crude songs of the young birds and the loud, clear, splendidly intoned and executed trills of these trained musicians!” So perhaps subsong singers fear ridicule. Or maybe the young birds aren’t ready to be on an equal conversational footing with adults.

  Subsong may be related to babbling, an activity that used to be considered a special human thing. But baby pygmy marmosets (tiny monkeys) babble incessantly, starting at two weeks, and add new sounds to their babble. Adult marmosets dote more when babies babble. As babies get older they babble less and get better at making the same kinds of sounds as grown marmosets.

  It has recently been noticed by linguists that small human children may be better talkers than they show. In at least some cases, toddlers talking to themselves in the privacy of their cribs (but being taped) say longer, more complicated things and use grammatical forms they didn’t use when talking with a parent half an hour earlier. There could be many reasons why a child might reserve this sophisticated chitchat for when it is alone, and it is interesting to wonder which might apply to subsong and other solo babble in nonhuman animals.

  Only child, only bird, only living being in the world

  A common method of studying birdsong has been to raise birds in isolation, often in soundproof chambers, so that their song cannot have been influenced by anything except what the experimenter chooses. Birdsong researchers West, King, and Freeberg note that although it has been known for decades that primates raised in isolation suffered from “clear and often irreversible deficits,” no one seems to have worried about birds raised in isolation. “Were birds considered cognitively or socially less complex than primates and therefore less likely to suffer social deficiencies?” The focus on studying only the song of the isolated bird, and not the bird itself, may have caused researchers to miss important factors in the way a bird develops song.

  When male white-crowned sparrow chicks grow up in isolation, they produce an “isolate song.” This pathetic ditty consists of scratchy primitive syllables. After a certain point it is too late for them to learn better, and they will be stuck with the isolate song forever.

  At the California Academy of Sciences, where scientists like the late Luis Baptista study birdsong, the bushes nearby are conveniently thronged with white-crowned sparrows. For several years a male called Weirdo held a territory there. While most of the white-crowns in the area sang the song associated with the nuttalli subspecies or the song associated with the gambeli subspecies, and a tiny minority sang pugetensis, Weirdo sang an isolate song, busily cranking out tasteless squeaks. How Weirdo grew up without hearing any sparrow song is unknown. But despite theories that the complexity, style, and vocal pyrotechnics of male song serve to attract females and discourage rivals, Weirdo had a desirable territory, and a charming wife, with whom he produced adorable nestlings.

  The sound of a woman’s voice

  There are also exceptions to the notion that male birds sing and females keep their beaks shut. Female and male cardinals both sing, but they handle matters differently. Girl and boy cardinals both learn songs on their father’s territory, and then the females stop, while the males learn more in the area where they set up their own territory. As a result, the female has the accent of her hometown, whereas the male sings like the other guys on his new block.

  In some species where it was thought that only males sang, it’s been discovered that females sing too, but not at the nest and not in breeding season, which is precisely when birdsong had been studied.

  For years, white-crowned sparrow females were not believed to sing. Except once in a while. Or if you shot them full of testosterone. Biologists who studied a lowland subspecies of white-crowns found that the females sing in autumn, winter, and early spring, stopping when nesting season begins. Females of a mountain subspecies arrived singing in early summer and clammed up except for periods of late snow melt, when nest sites were hard to come by and competition was particularly savage.

  Researchers characterized the female songs as shorter, softer, quavery, and lacking some terminal syllables. Sometimes the females had countersinging matches with their mates, and when they did, their songs were like male songs. Female 17, for example, had only simple syllables in her songs, but one day “she dominated and chased her mate,…c
ountersang with him and subsequently sang a second theme containing a complex syllable similar to those in his song.” Female 18 had a fight with her mate and, instead of her usual simple-syllabled song, sang one that matched his.

  Female white-crowns accompanied singing with territorial behavior such as attacking and chasing other birds. Female 8 was widowed and sang frequently and loudly for over two weeks, until she met male BK/S, whereupon she hushed and the two got to work building a nest, suggesting that she had been singing to advertise for a mate.

  So in a nest of baby white-crowned sparrows, both the female and male nestlings are listening to their father’s song and committing it to memory. Although their mother can sing, the babies presumably have no inkling of this, since she is silent during the breeding season.

  Learning the wrong songs

  Birds learn the songs of their species, except when they don’t. In a mountain meadow in the Sierra Nevada, researchers studying the white-crowned sparrow heard its familiar notes coming from a Lincoln sparrow. Fascinated, they recorded the singer. The bird sang five different themes (unique combinations of syllables), three of which contained syllables from typical white-crowned sparrow song. How did this happen? In the meadow there were 25 pairs of white-crowns and only two of Lincoln sparrows. Maybe when it was young this bird didn’t hear many Lincoln sparrows, so in its quest for variety it picked up syllables from the white-crowned sparrow songs it heard on every side.

  New neurons

  When songbirds learn new songs on new territories, or to compete with new neighbors, they may be aided by new neurons they have grown for the purpose. It was once believed that creatures never acquired new neurons after birth, but Fernando Nottebohm and colleagues, working with canaries, have shown that males grow new neurons each spring in the part of the brain they use for learning song. Over the summer that area shrinks, but it expands again in the fall when the birds learn new songs. Moving on to chickadees, Nottebohm found that they grow new hippocampal neurons in the fall, when they need to remember where they stored the thousands of seeds they’ll eat in the winter.