When baby kākāriki first emerge from the egg, they’re not exactly pretty: they have huge blind eyes, prominent beaks, and bony, naked necks. Their bodies are an untidy melange of pink skin and grey feathers. But their primary-coloured adult plumage grows quickly, and a month later, they’re ready to leave the nest.
For the first week, fledging kākāriki stick around home and are still fed by their parents, says Zealandia Ecosanctuary’s Ellen Irwin, who radio-tracked 22 juvenile kākāriki for her master’s research at Te Herenga Waka/Victoria University of Wellington. At this crucial moment in the young birds’ lives, she says, you could almost mistake them for adults—but they still have a lot to learn.
“They tend to be quite uncoordinated,” says Irwin. “They don’t totally know how to fly, they’ll stumble a bit or kind of flap their wings awkwardly. Or they’ll pick up something to eat and accidentally drop it. They’re a little bit awkward as they’re trying to figure out their way in the world—and that puts them at great risk of predation, flying into windows, or not being able to feed themselves.”
One young kākāriki she tracked flew over Zealandia’s predator-proof fence into an unprotected reserve, then took a nap on the ground. “It wasn’t making the best decisions.”
Animals, like humans, are not born adult. They start life vulnerable and clueless and needing protection, and must acquire the experiences and skills necessary to navigate the world as a functional adult. In humans, we call this period being teen, or adolescence—though the latter term refers more to the physical (being fully grown) than the mental or emotional (being fully grown up).
In a recent book, UCLA evolutionary biologist Barbara Natterson-Horowitz and science journalist Kathryn Bowers propose a new term for this period—‘wildhood’—and argue that this formative, dangerous, exhilarating time has been a feature of life on Earth for the past 600 million years.
In the Burpee Museum of Natural History in Rockford, Illinois, you can see the bones of two teenage, horse-sized Tyrannosaurus rex, Jane and Petey, who died 66 million years ago while still growing rapidly. Primitive protozoa like the malaria parasite go through puberty. And even the first strange, soft-bodied animals that teemed in the primeval Ediacaran ocean had to grow up.
“Adolescence is a challenging time, for parents and teens alike,” the Wildhood authors write. “But you’re not alone. From humpback whales to hummingbirds, young animals across the wild world are facing the same challenges.”
These surprisingly universal trials are four-fold, they argue. Whether a young animal’s wildhood lasts days, weeks or years, it must learn how to stay safe, how to navigate social hierarchies, how to leave the nest and care for itself, and how to communicate sexually.
Adult humans have eye-rolled about teenagers’ thrill-seeking and intensity for millennia. “They would always rather do noble deeds than useful ones,” complained Aristotle in 400BC. “All their mistakes are in the direction of doing things excessively and vehemently. They overdo everything—they love too much, hate too much.” Shakespeare cast similar aspersions: “I would there were no age between 10 and three-and-twenty, or that youth would sleep out the rest; for there is nothing in the between but getting wenches with child, wronging the ancientry, stealing, fighting.” There’s even a word for this fear or dislike of youth: ephebiphobia.
It’s kind of strange that it’s socially acceptable to mock and demonise teenagers, points out Sarah-Jayne Blakemore, a cognitive neuroscientist at University College London and the University of Cambridge, and the author of a book on the teenage brain. “What’s sometimes seen as the problem with adolescence—heightened risk-taking, poor impulse control, self-consciousness—shouldn’t be stigmatised,” she said in a 2012 TED talk. “It actually reflects changes in the brain that provide an excellent opportunity for education and social development.”
Like the ground-snoozing kākāriki, many young animals don’t have an innate sense of stranger-danger and must develop predator awareness and avoidance strategies through experience. Sometimes, the best way to learn is to actively put yourself in the line of fire, as a study of Thomson’s gazelles in the Serengeti showed.
Researchers noticed that gazelles would sometimes move towards a stalking cheetah rather than hiding or running away—a behaviour called ‘predator inspection’, which is also found in other prey species, including sea otters, meerkats and bats.
Such risky behaviour has consequences; in one study, adolescent gazelles following a cheetah were attacked and killed in one out of 417 approaches. (The probability of death was only one in 5000 for more experienced, adult gazelles.)
And yet, the fact that predator inspection exists means it must be adaptive, says Bowers. Young gazelles gain crucial knowledge about their predators from their own near misses, she theorises, and from the mistakes of their friends.
“Some of them will die, but the ones that survive have learned a really important lesson about how that cheetah smells, how it moves, what time of day it’s most likely to chase them, which way to run, and how if you’re in a group you’re safer—they get a lot of really good information.”
Studies of humans show that foolhardy behaviour like dangerous driving increases when adolescents are hanging out with their friends. “The new neuroscience shows that social influence has the biggest effect on adolescent decision-making and risk-taking,” says Blakemore. And that’s not necessarily a bad thing, adds Bowers. “Your parents have good intentions, but they don’t always know what the dangers are in the contemporary world that you’re in.”
The prevalence of predator inspection and similar behaviours in the animal world shows there may be an evolutionary basis to teenage irresponsibility, she says. Accidents certainly happen, but the insights from the animal world suggest that facing threats together with peers, for the most part, makes adolescents safer in the long run.
Often, though, it falls to adults to help adolescent animals become upstanding members of their community.
Bottlenose dolphins’ extended period of adolescence (about seven to eight years) functions as an apprenticeship in group behaviour, says University of Auckland marine biologist Rochelle Constantine.
This knowledge can be hard-won. Adolescent dolphins frequently get into trouble with their mothers and other adults for misbehaving. It’s especially noticeable when the pod is resting—or trying to.
“When you see a group of dolphins resting, the juveniles will often be jumping, rolling around on the adults, zipping about, chasing things.” That’s a problem, Constantine says. These periods of rest, when dolphins put half their brain to sleep for a while, are crucial for individual and group wellbeing. From the adults’ perspective, these hell-raising youngsters “are pretty darned annoying”, she says.
“Sometimes you’ll see one adult go off at speed, chase up all the juveniles and bring them back to the group”—almost as though they were getting “a severe telling off”. When an adolescent bottlenose behaves particularly badly, its mother will pin it to the sea bed with her body as punishment—the cheeky young dolphin getting literally grounded.
Adults might find them irritating, but constant play and pushing boundaries are how young dolphins learn. Constantine has watched juveniles amusing themselves with turtles—“even if the turtle doesn’t want to be played with”. She’s seen them horsing around with young humpback whales, riding the larger animals’ bow waves, and trying and failing to eat pufferfish—with a look of utmost surprise on their faces when the fish releases toxins from its spines.
Navigating the social world also involves discerning—and attempting to manipulate—your place in the hierarchy of your peers, write Natterson-Horowitz and Bowers. “Obsession with status, it turns out, is entirely natural.” Hyenas indulge in “friendship walking” to cement their relationships, wandering around in pairs sniffing at the same things. High-status chickens apparently experience the “joy of satisfied pecking-lust” while their lowly flockmates are “dulled by a premonition of hopelessness”, according to Thorleif Schjelderup-Ebbe, the Norwegian zoologist who first described the pecking order after studies he began as a young boy in 1901.
One much more recent study of rhesus macaques showed they would give up a drink of sweet juice for the chance to watch a high-status macaque on a screen—and they showed no such interest in the activities of low-status monkeys. In fact, the scientists had to bribe them with extra juice just to keep watching.
For Natterson-Horowitz and Bowers, such studies suggest that if social creatures such as macaques, hyenas, humpbacks or hummingbirds had access to a species-appropriate form of social media, they would be just as hopelessly addicted as we are.
“We’ve intensified and amplified the sort of natural social anxiety that many animals have,” says Bowers, “the same way that we’ve refined and distilled drugs and alcohol to make them more powerful and to last longer and to be available throughout the year.”
Humans aren’t uniquely bad at impulse control, she says. Plenty of animals overindulge in intoxicants if given the chance—lemurs lick toxic millipedes, reindeer deliberately forage for magic mushrooms, bighorn sheep in the Canadian Rockies will walk tightrope over narrow ledges to reach patches of narcotic lichen, Tasmanian wallabies get so high eating opium poppies that they can no longer hop in a straight line, creating crop circles—and in summer 2010, the Whangārei Native Bird Recovery Centre treated 25 kererū that had injured themselves while drunk on overripe guavas.
According to the Whangārei Leader, some were so wasted they vomited up bright-red guava juice. The reports didn’t say how many of them were adolescents.
Wildhood is also the time when an animal has its first sexual experiences. “You might not have had many opportunities to think about moth virginity,” write Natterson-Horowitz and Bowers. Well, no. But now that we are, let me tell you about Ostrinia nubilalis—an agricultural pest dubbed the European corn borer. These moths express sexual receptivity and desire to each other using a complex set of behaviours including fanning, circling, bowing, kneeling, and embracing.
Researchers observed the first sexual encounters of 252 virgin corn borer moths and found that they were “full of fumblings and missteps”. The inexperienced moths were awkward, still figuring out how to read sexual signals and respond appropriately—a familiar sensation for anyone who has ever been a teenager.
That near-universal feeling is perfectly evoked by a single word in the Yaghan language of South America’s Tierra del Fuego, the Wildhood authors explain—a language which is rich in words to describe very specific kinds of awkwardness. Mamihlapinatapai means, roughly, “a look shared by two people, each wishing the other would initiate something that they both desire but which neither knows how to begin”,—though not necessarily in a sexual or romantic context.
The ways animals try to assess whether they actually want to get it on are as colourful and varied as a bird-of-paradise’s feathers. Adult bald eagles, for instance, grasp each other’s talons mid-air and tumble spiralling from the sky like a pair of figure skaters. Like the ballroom dances in Pride and Prejudice or Bridgerton, the spiral seems to give the eagles a chance to check their chemistry—and get a sense of whether the other is willing, and ready, to pair up. Adolescent eagles, meanwhile, have to practise the manoeuvre, failing the catch often before they manage to pull it off.
Most of the time, a rejected animal will take no for an answer. But nature is no consensual utopia. Sexual coercion happens in at least 43 species, including some types of insects, fish, birds, reptiles, and mammals. Male bottlenose dolphins, for instance, will gang up to force a lone female into sex. Pressure isn’t always physical—male chimpanzees have been observed to harass females so thoroughly they agree to mating “because the costs of saying no are so high”, says Bowers, who sees resonances with the #MeToo movement that swept the US as she and Natterson-Horowitz worked on their book. Similarly, male water striders will make a nuisance on the water, creating ripples that attract predatory fish, until a female accepts their advances out of fear for her life.
Some adolescent female animals resort to creative extremes to avoid unwanted male attention. The fossa (Cryptoprocta ferox—the name means ‘ferocious animal with a hidden anus’) is a cat-like lemur-eating apex predator on the island of Madagascar. When young female fossas hit puberty, some undergo a temporary sex change —their clitorises begin to resemble the spiny penis of the fossa male, and their testosterone spikes—presumably changing their behaviour as well.
Scientists don’t yet know how often this happens, or why, but Natterson-Horowitz speculates that the fossas are effectively dressing as a man for their own protection—a strategy frequently deployed by human women throughout history. “Younger females are at greater risk for sexual coercion, and it may be an adaptation to protect them during that vulnerable period—because then they revert to the fully female phenotype later in life.”
When young creatures have learned everything they can from their parents, it’s time to leave the nest. In some species, like king penguins, hormonal changes in the brain induce a sense of zugunruhe, or ‘migration anxiety’—a thrilling sense that it’s time to leap from the ice shelf and strike out into the unknown. Other adolescents are literally driven away by their parents. Adult imperial eagles in Spain start by denying food to their overstaying offspring, but then get even meaner: they dive-bomb the lingering youngsters until they get the message and move away.
For many species, conflict between parents and children peaks around this time of dispersal—a finding Natterson-Horowitz found reassuring while parenting her own almost-fledged teenagers. Some mammals, though, patiently train their young to leave home in a series of phased steps.
Researchers studying brushtail possums in their natural habitat in South Australia observed that joeys would start by riding on their mother’s back, graduate to running at her feet, and finally head out for a solo sleepover at a nearby tree. Once they’ve passed that test, and the mother is satisfied they can feed themselves, they’re ready to leave home.
But one possum mother kept an adolescent male with her long after his siblings dispersed, spending more time teaching him the ropes of possumhood. For Bowers, the story highlights that wildhood isn’t one size fits all. Although it is an almost-universal process, there is individual variation in how fast it unfolds—just as some adolescent humans stride out the door at 17, while others spend a little longer under their parents’ roof.
In Wellington, Irwin—not long out of her own wildhood at the time—walked 20 kilometres a day, tracking the young kākāriki as they left Zealandia and went out into the world—or not. “Some dispersed really far away and settled outside the sanctuary, while others were sort of homebodies that stuck really close to where they hatched.” A third group seemed indecisive, flitting out to a particularly lush fruiting tōtara to feed and then returning to Zealandia at night.
Things got real out there in the big wide world. A third of the juveniles that dispersed outside the sanctuary during Irwin’s study were killed by predators, while those inside the sanctuary stayed safe. The adventurers that survived, however, would have spent their wildhood nailing down those four big universal lessons—safety, status, self-reliance, and sex.
For Natterson-Horowitz and Bowers, researching Wildhood was oddly comforting. “This idea that evolution has your back—that even though it’s a difficult time of life, it’s kind of difficult for a reason,” says Bowers. The trials and experiences of wildhood forge us into healthy, creative, and resilient adults. Being teen is necessarily tumultuous—and that’s normal, not just for humans, but for the vast tribe of adolescents swimming and climbing and burrowing and flying their way into adulthood the world over.