An award-winning science writer tours the globe to reveal what makes birds capable of such extraordinary feats of mental prowess
Birds are astonishingly intelligent creatures. According to revolutionary new research, some birds rival primates and even humans in their remarkable forms of intelligence. In The Genius of Birds, acclaimed author Jennifer Ackerman explores their newly discovered brilliance and how it came about.
As she travels around the world to the most cutting-edge frontiers of research, Ackerman not only tells the story of the recently uncovered genius of birds but also delves deeply into the latest findings about the bird brain itself that are shifting our view of what it means to be intelligent. At once personal yet scientific, richly informative and beautifully written, The Genius of Birds celebrates the triumphs of these surprising and fiercely intelligent creatures.
Ackerman is also the author of Birds by the Shore: Observing the Natural Life of the Atlantic Coast.
|Publisher:||Penguin Publishing Group|
|Product dimensions:||5.40(w) x 8.30(h) x 0.90(d)|
About the Author
JENNIFER ACKERMAN has been writing about science, nature, and human biology for almost three decades. Her most recent books include Sex Sleep Eat Drink Dream: A Day in the Life of Your Body; Ah-Choo: The Uncommon Life of Your Common Cold; Chance in the House of Fate: A Natural History of Heredity; and Notes from the Shore. A contributor to Scientific American, National Geographic, The New York Times, and many other publications, Ackerman is the recipient of a National Endowment for the Arts Literature Fellowship in Nonfiction, a Bunting Fellowship, and a grant from the Alfred P. Sloan Foundation.
Read an Excerpt
THE GENIUS OF BIRDS
For a long time, the knock on birds was that they’re stupid. Beady eyed and nut brained. Reptiles with wings. Pigeon heads. Tur- keys. They fly into windows, peck at their reflections, buzz into power lines, blunder into extinction.
Our language reflects our disrespect. Something worthless or un- appealing is “for the birds.” An ineffectual politician is a “lame duck.” To “lay an egg” is to flub a performance. To be “henpecked” is to be ha- rassed with persistent nagging. “Eating crow” is eating humble pie. The expression “bird brain,” for a stupid, foolish, or scatterbrained person, en- tered the English language in the early 1920s because people thought of birds as mere flying, pecking automatons, with brains so small they had no capacity for thought at all.
That view is a gone goose. In the past two decades or so, from fields and laboratories around the world have flowed examples of bird species capable of mental feats comparable to those found in primates. There’s a kind of bird that creates colorful designs out of berries, bits of glass, and blossoms to attract females, and another kind that hides up to thirty- three thousand seeds scattered over dozens of square miles and remem- bers where it put them months later. There’s a species that solves a classic puzzle at nearly the same pace as a five-year-old child, and one that’s an expert at picking locks. There are birds that can count and do simple math, make their own tools, move to the beat of music, comprehend basic prin- ciples of physics, remember the past, and plan for the future.
In the past, other animals have gotten all the publicity for their near- human cleverness. Chimps make stick spears to hunt smaller primates and dolphins communicate in a complex system of whistles and clicks. Great apes console one another and elephants mourn the loss of their own.
Now birds have joined the party. A flood of new research has over- turned the old views, and people are finally starting to accept that birds are far more intelligent than we ever imagined—in some ways closer to our primate relatives than to their reptilian ones.
Beginning in the 1980s, the charming and cunning African grey par- rot named Alex partnered with scientist Irene Pepperberg to show the world that some birds appear to have intellectual abilities rivaling those of primates. Before Alex died suddenly at the age of thirty-one (half his expected life span), he had mastered a vocabulary of hundreds of English labels for objects, colors, and shapes. He understood the categories of same and different in number, color, and shape. He could look at a tray holding an array of objects of various colors and materials and say how many there were of a certain type. “How many green keys?” Pepperberg would ask, displaying several green and orange keys and corks. Eight out of ten times, Alex got it right. He could use numbers to answer questions about addition. Among his greatest triumphs, says Pepperberg, were his knowledge of abstract concepts, including a zerolike concept; his capacity to figure out the meaning of a number label from its position in the num- ber line; and his ability to sound out words the way a child does: “N-U-T.” Until Alex, we thought we were alone in our use of words, or almost alone. Alex could not only comprehend words, he could use them to talk back with cogency, intelligence, and perhaps even feeling. His final words to Pepperberg as she put him back in his cage the night before he died were his daily refrain: “You be good, see you tomorrow. I love you.”
In the 1990s, reports began to roll in from New Caledonia, a small is- land in the South Pacific, of crows that fashion their own tools in the wild and appear to transmit local styles of toolmaking from one genera- tion to the next—a feat reminiscent of human culture and proof that so- phisticated tool skills do not require a primate brain.
When scientists presented these crows with puzzles to test their problem-solving abilities, the birds astonished them with their crafty solutions. In 2002, Alex Kacelnik and his colleagues at Oxford University “asked” a captive New Caledonian crow named Betty, “Can you get the food that’s out of reach in a little bucket at the bottom of this tube?” Betty blew away the experimenters by spontaneously bending a piece of wire into a hook tool to pull up the little bucket.
Among the published studies tumbling from scientific journals are some with titles that lift the brows: “Have we met before? Pigeons recog- nize familiar human faces”; “The syntax of gargles in the chickadee”; “Language discrimination by Java sparrows”; “Chicks like consonant music”; “Personality differences explain leadership in barnacle geese”; and “Pigeons on par with primates in numerical competence.”
Bird brain: The slur came from the belief that birds had brains so diminutive they had to be devoted only to instinctual behavior. The avian brain had no cortex like ours, where all the “smart” stuff happens. Birds had minimal noggins for good reason, we thought: to allow for airborne ways; to defy gravity; to hover, arabesque, dive, soar for days on end, migrate thousands of miles, and maneuver in tight spaces. For their mas- tery of air, it seemed, birds paid a heavy cognitive penalty.
A closer look has taught us otherwise. Birds do indeed have brains very different from our own—and no wonder. Humans and birds have been evolving independently for a very long time, since our last com- mon ancestor more than 300 million years ago. But some birds, in fact, have relatively large brains for their body size, just as we do. Moreover, when it comes to brainpower, size seems to matter less than the number of neurons, where they’re located, and how they’re connected. And some bird brains, it turns out, pack very high numbers of neurons where it counts, with densities akin to those found in primates, and links and con- nections much like ours. This may go a long way toward explaining why certain birds have such sophisticated cognitive abilities.
Like our brains, the brains of birds are lateralized; they have “sides” that process different kinds of information. They also have the ability to replace old brain cells with new ones just when they’re needed most. And although avian brains are organized in an entirely different way from our brains, they share similar genes and neural circuits, and are capable of feats of quite extraordinary mental power. To wit: Magpies can recog- nize their own image in a mirror, a grasp of “self” once thought limited to humans, great apes, elephants, and dolphins and linked to highly devel- oped social understanding. Western scrub jays use Machiavellian tactics to hide their food caches from other jays—but only if they’ve stolen food themselves. These birds seem to have a rudimentary ability to know what other birds are “thinking” and, perhaps, to grasp their perspective. They can also remember what kind of food they buried in a particular place— and when—so they can retrieve the morsel before it spoils. This ability to remember the what, where, and when of an event, called episodic mem- ory, suggests to some scientists the possibility that these jays may be able to travel back into the past in their own minds—a key component of the kind of mental time travel once vaunted as uniquely human.
News has arrived that songbirds learn their songs the way we learn languages and pass these tunes along in rich cultural traditions that began tens of millions of years ago, when our primate ancestors were still scut- tling about on all fours. Some birds are born Euclideans, capable of using geometric clues and landmarks to orient themselves in three-dimensional space, navigate through unknown territory, and locate hidden treasures. Others are born accountants. In 2015 researchers found that newborn chicks spatially “map” numbers from left to right, as most humans do (left means less; right means more). This suggests that birds share with us a left-to-right orientation system—a cognitive strategy that underlies our human capac- ity for higher mathematics. Baby birds can also understand proportion and can learn to choose a target from an array of objects on the basis of its ordinal position (third, eighth, ninth). They can do simple arithmetic, as well, such as addition and subtraction. Bird brains may be little, but it’s plain they punch well above their weight.
Birds have never seemed dumb to me. In fact, few other creatures appear so alert, so alive in fiber and faculty, so endowed with perpetual oomph. Sure, I’ve heard the story of the raven attempting to crack open a Ping-Pong ball, presumably to get at an egglike morsel within. A friend of mine, while vacationing in Switzerland, watched a peacock try to fan its broad tail during a mistral. It toppled over, stood upright again, fanned again, and tipped over again, six or seven times in a row. Each spring the robins nesting in our cherry tree attack the side mirror of our car as if it were a rival, pecking furiously at their own reflections while streaking the door with guano.
But who among us hasn’t been toppled by our own vanity or made an enemy of our own image?
I’ve watched birds most of my life and have always admired their pluck and focus and the taut, quick vitality that seems almost too much for their tiny bodies to contain. As Louis Halle once wrote, “A man would be worn out in short order by such intensity of living.” The common species I saw around my old neighborhood appeared to negotiate the world with brisk curiosity and aplomb. The American crows striding around our garbage cans with a prince’s proprietary air looked like highly resourceful creatures. I once watched a crow stack two crackers in the middle of a road before flying off to a safe spot to devour his collected booty.
One year, an eastern screech owl roosted in a box on a maple tree just a few yards from my kitchen window. In the daylight hours, the owl slept, only its round head showing, perfectly framed in the round hole facing the window. But at night, the owl was gone from the box, off hunting in the night. As the dawn light rose, there were signs of his brilliant success— the wing of a mourning dove or songbird hanging from the hole of the box, twitching, twitching, before it was yanked inside.
Even the red knots I encountered on the beaches of Delaware Bay, not the mentally swiftest of birds, seemed to know where to be—and when— to catch the rich feast of eggs laid by horseshoe crabs each full moon in spring. What calendar of sky drew these birds northward and told them where to go?
I learned about birds from a pair of Bills. The first was my father, Bill Gorham, who began taking me birdwatching near our home in Wash- ington, D.C., when I was seven or eight. It was the Beltway version of a Swedish gökotta—the act of rising early to appreciate nature—and it was one of the palpable joys of my childhood. On early weekend mornings in spring we left the house in the dark and headed to the woods along the Potomac River to catch the dawn chorus, that mysterious moment when birds sing with a thousand voices in “A Music numerous as space— / But neighboring as Noon,” as Emily Dickinson wrote.
My father learned about birds as a Boy Scout from a nearly blind man named Apollo Taleporos. The old man relied on his ears alone to pick up species. Parula warbler. Yellow-rumped warbler. Towhee. “The birds are there!” he would call out to the boys. “Go find them!” My father got very good at identifying birds by their calls—the melodious flutelike song of the wood thrush, the soft whichity, whichity of a common yellowthroat, or the clear whistling call of a white-throated sparrow.
As my father and I wandered through the woods in late starlight, I would listen to the husky song of a Carolina wren and wonder what, if anything, those birds were saying, and how they learned their songs. Once, I encountered a young white-crowned sparrow apparently engaged in song practice. There he was, perched invisibly somewhere in a low branch of a cedar tree, softly running through his whistles and trills, getting them wrong, and then going back over them quietly and persistently until he delivered the final run of his kind. This sparrow, I later learned, gleans his songs not from his own father but from birds in his natal environment, that very neighborhood of woods and rivers where my father and I rambled—a place with its own dialect passed down through the generations.
The other Bill I met at the Sussex Bird Club when I lived in Lewes, Delaware. Bill Frech was up and out of the house every morning at five a.m. for four or five hours of watching shorebirds and those little brown jobs, or LBJs, common in the woods and fields around Lewes. A patient, devoted, and inexhaustible observer, he kept meticulous notes on what birds he saw, where, and when, which ended up at the Delmarva Orni- thological Society as part of the state’s official bird records. This Bill was nearly deaf, but he was a wizard at identifying birds visually, by their so-called GISS, their general impression, size, and shape. He showed me how to spot a goldfinch high on the wing by its dipping flight and how to tell shorebirds apart by noting their personality, behavior, and gestalt, just as one recognizes friends from a distance by their overall manner and gait. He taught me the difference between casual “birdwatching” and the more intense, focused “birding,” and urged me to go beyond identifying birds to noting their actions and behavior.
The birds I observed on those excursions and others seemed to know what they were doing. Like the black-billed cuckoo a friend saw perched just above a nest of tent caterpillars: The cuckoo waited as the caterpillars climbed out of the nest to scale the tree, then plucked them off one at a time, like sushi from a conveyor belt.Still, I never imagined that the magpies and jays, the chickadees and herons, I admired so much for their feathers and flight, their songs and calls, might have mental abilities that match—even exceed—those in my primate tribe. How can creatures with a nut-sized brain perform such sophisticated mental feats? What has shaped their intelligence? Is it the same or differ- ent from ours? What, if anything, do their little brains have to tell us about our big ones?
Intelligence is a slippery concept, even in our own species, tricky to define and tricky to measure. One psychologist describes it as “the capac- ity to learn or to profit by experience.” And another, as “the capacity to acquire capacity”—the same sort of circular definition offered up by Har- vard psychologist Edwin Boring: “Intelligence is what is measured by in- telligence tests.” As Robert Sternberg, a former dean at Tufts University, once quipped, “There seem to be almost as many definitions of intelli- gence as . . . experts asked to define it.”
In judging the overall intelligence of animals, scientists may look at how successful they are at surviving and reproducing in many different environments. By this measure, birds trump nearly all vertebrates, includ- ing fish, amphibians, reptiles, and mammals. They are the one form of wildlife visible nearly everywhere. They live in every part of the globe, from the equator to the poles, from the lowest deserts to the highest peaks, in virtually every habitat, on land, sea, and in bodies of freshwater. In biological terms, they have a very big ecological niche.
As a class, birds have been around for more than 100 million years. They are one of nature’s great success stories, inventing new strategies for survival, their own distinctive brands of ingenuity that, in some respects at least, seem to far outpace our own.
Somewhere in the mists of deep time lived the überbird, the common ancestor of all birds, from hummingbird to heron. Now there are some 10,400 different bird species—more than double the number of mammal species: thick-knees and lapwings, kakapos and kites, hornbills and shoe- bills, chukars and chachalacas. In the late 1990s, when scientists estimated the total number of wild birds on the planet, they came up with 200 to 400 billion individual birds. That’s roughly 30 to 60 live birds per person. To say that humans are more successful or advanced really depends on how you define those terms. After all, evolution isn’t about advancement; it’s about survival. It’s about learning to solve the problems of your envi- ronment, something birds have done surpassingly well for a long, long time. Which to my mind makes it all the more surprising that many of us—even those of us who love them—have found it hard to swallow the idea that birds may be bright in ways we can’t imagine.
Perhaps it’s because they’re so unlike people that it’s difficult for us to fully appreciate their mental capabilities. Birds are dinosaurs, de- scended from the lucky, flexible few that survived whatever cataclysm did in their cousins. We are mammals, related to the timid, diminutive shrew- like creatures that emerged from the dinosaurs’ shadows only after most of those beasts died off. While our mammal relatives were busy growing, birds, by the same process of natural selection, were busy shrinking. While we were learning to stand up and walk on two feet, they were perfecting lightness and flight. While our neurons were sorting them- selves into cortical layers to generate complex behavior, birds were devis- ing another neural architecture altogether, different from a mammal’s but—in some ways, at least—equally sophisticated. They, like us, were figuring out how the world works, and all the while, evolution was fine-tuning and sculpting their brains, giving their minds the magnificent powers they have today.
Birds learn. They solve new problems and invent novel solutions to old ones. They make and use tools. They count. They copy behaviors from one another. They remember where they put things.
Even when their mental powers don’t quite match or mirror our own complex thinking, they often contain the seeds of it—insight, for instance, one of our big-ticket cognitive abilities, which has been defined as the sudden emergence of a complete solution without trial-and-error learn- ing. It often involves mental simulation of a problem and a kind of “aha!” moment when the solution becomes apparent in a flash of understanding. Whether birds have actual insight remains to be determined, but certain species seem to understand cause and effect—one of the building blocks of insight. The same is true for “theory of mind,” a nuanced understand- ing of what another individual knows or thinks. Whether birds possess
this full-blown ability is debatable, but members of certain species seem to be able to take the perspective of another bird or sense its needs, neces- sary components of theory of mind. Some scientists call these building blocks or stepping-stones the signatures of cognition and believe they may be the precursors to such highly complex human cognitive abilities as rea- soning and planning, empathy, insight, and metacognition—awareness of one’s own thought processes.
Of course, these are all human yardsticks of intelligence. We can’t help but measure other minds against our own. But birds also possess ways of knowing beyond our ken, which we can’t easily dismiss as merely instinc- tual or hardwired. What kind of intelligence allows a bird to anticipate the arrival of a distant storm? Or find its way to a place it has never been before, though it may be thousands of miles away? Or precisely imitate the complex songs of hundreds of other species? Or hide tens of thousands of seeds over hun- dreds of square miles and remember where it put them six months later? (I would flunk these sorts of intelligence tests as readily as birds might fail mine.)
Maybe genius is a better word. The term comes from the same root as gene, derived from the Latin word for “attendant spirit present from one’s birth, innate ability or inclination.” Later, genius came to mean natural ability, and finally (thanks to the essay “Genius” by Joseph Addison in 1711) to denote exceptional talent, natural or learned. More recently, genius has been defined as “nothing more nor less than doing well what anyone can do badly.” It’s a mental skill that’s exceptional compared with others, either of your kind or another kind. Pigeons have a genius for navigation that far, far exceeds our own. Mockingbirds and thrashers can learn and remember hundreds more songs than most of their fellow songbird species. Scrub jays and nutcrackers have memories for where they put things that make our capacity look meager.
In this book, genius is defined as the knack for knowing what you’re doing—for “catching on” to your surroundings, making sense of things, and figuring out how to solve your problems. In other words, it’s a flair for meeting environmental and social challenges with acumen and flexibility, which many birds seem to possess in abundance. Often this involves doing something innovative, something new—taking advan- tage of a new food source, for instance, or learning how to exploit it. The classic example of this was demonstrated years ago by tits in the United Kingdom. Both great tits and blue tits picked up the knack of opening the cardboard caps of milk bottles delivered to people’s doorsteps in the morning to get at the rich cream on top. (Birds can’t digest the carbohy- drates in milk, only the lipids.) The tits first learned the trick in 1921 in the town of Swaythling; by 1949, the behavior had been noted in hundreds of localities throughout England, Wales, and Ireland. The technique had apparently spread by one bird copying another—an impressive show of social learning.
The misguided use of “bird brain” as a slur has finally come home to roost. One by one, the bellwether differences between birds and our closest primate relatives seem to be falling away—toolmaking, culture, reasoning, the ability to remember the past and think about the future, to adopt another’s perspective, to learn from one another. Many of our cherished forms of intellect—whether in whole or parts—appear to have evolved in birds quite separately and artfully right alongside our own. How can this be? How can creatures separated by a 300-million-year gulf of evolution have similar cognitive strategies, skills, and abilities?
For one thing, we share more biology with birds than one might think. Nature is a master of bricolage, hanging on to biological bits that are useful and modifying them for new purposes. Many of the changes that separate us from other creatures have arisen not through the evolution of new genes or cells but through subtle shifts in how existing ones are used. This shared biology is what makes it possible to use other organ- isms as model systems to understand our own brains and behavior— to study learning in the giant sea snail Aplysia, anxiety in zebra fish, obsessive-compulsive disorder in border collies.
We also share with birds similar ways of meeting nature’s challenges, which we’ve arrived at through very different evolutionary paths. It’s called convergent evolution, and it’s rampant in the natural world. The convergent shape of wings in birds, bats, and the reptiles known as ptero- saurs results from the problems posed by flight. To meet the challenges of filter feeding, creatures as far apart on the tree of life as baleen whales and flamingos show striking parallels in behavior, body form (large tongues and hairy tissues known as lamellae), even body orientation during feeding. As evolutionary biologist John Endler points out, “Again and again, in totally unrelated groups, we find many instances of conver- gence in form, appearance, anatomy, behavior and other aspects. So why not in cognition, too?”
That both humans and certain species of birds have evolved brains large for their body size almost certainly represents convergent evolu- tion. Likewise, the evolution of the same patterns of brain activity during sleep. And similarly, the evolution of analogous brain circuits and pro- cesses for learning song and speech. Darwin called birdsong “the nearest analogy to language.” He was right. The parallels are eerie. Especially when you consider the evolutionary distance between humans and birds. A group of two hundred scientists from eighty different labs recently of- fered a window on these parallels when they sequenced the genomes of forty-eight birds. Their results, published in 2014, revealed startlingly similar gene activity in the brains of humans learning to speak and birds learning to sing, suggesting that there may be a kind of core pattern of gene expression for learning shared by birds and humans alike and ar- rived at through convergent evolution.
For all these reasons, birds are turning out to be wonderful animal models for understanding how our brains learn and remember, how we create language, what mental processes might underlie our problem solv- ing, and how we locate ourselves in space and in social groupings. The circuits in the bird brain that control social behavior are much like the cir- cuits in our own brains, it turns out, run by similar genes and chemicals. By investigating the neurochemistry of a bird’s social nature, we stand to learn something about our own. Likewise, if we can grasp what’s going on in a bird’s brain as it masters a melody, we might get a better handle on how our own brains learn language, why it gets harder to master a new language over time, and maybe even how speech evolved in the first place. If we can understand why two animals so distantly related converged on the same pattern of brain activity during sleep, we might solve one of na- ture’s great mysteries—the purpose of sleep.
This book is a quest to understand the different sorts of genius that have made birds so successful—and how they came about. It’s a journey of sorts, venturing as far afield as Barbados and Borneo, as near as my own backyard. (You don’t need to travel to exotic locations or see exotic species to witness intelligence in birds. It’s everywhere around you, at your bird feeders, in local parks, city streets, and country skies.) It’s also a voyage into the brains of birds, right down to the cells and molecules that drive their thinking and, sometimes, ours. Each chapter tells the story of birds with extraordinary abilities or skills—technical, social, musical, artistic, spatial, inventive, adaptive. A few are exotic species; others, more common. You’ll see members of the supremely clever corvid and parrot families appear and reappear through- out these pages, but also the sparrow and the finch, the pigeon and the chickadee. I’m interested in the everyman of the bird world as well as the Einsteins. I might have chosen other species as my stars, but I chose these for a simple reason: They have great stories to tell, stories that illu- minate what might be going on in the mind of a bird as it solves the prob- lems around it—and also, perhaps, give us some perspective on what is going on in our own minds. All these birds stretch our thinking about what it means to be intelligent.
The final chapter focuses on the adaptive brilliance of certain birds. Only a relative few possess this genius. Changes in the environment— especially those induced by humans—throw a wrench into the lives of many birds and disrupt their keen ways of knowing. A recent report from Audubon tells us that half of the bird species in North America— from whip-poor-will to white-tailed kite, common loon to shoveler, pip- ing plover to dusky grouse—are likely to go extinct in the next half century or so for one reason: because they can’t adapt to the rapid pace of human-induced change on our planet. Which birds will survive and why? In what ways are we humans an evolutionary force selecting for a certain kind of bird and bird intelligence?
Scientists are coming at these puzzles from many different angles. Some are lifting the hood on the bird brain, using modern techniques to see what’s going on in a bird’s neural circuits when it recognizes a human face or to listen to individual brain cells as a songbird learns its song or to compare the neurochemicals in birds that are social butterflies with those that are loners. Some are sequencing and comparing bird genomes to pin- point genes involved in complex behaviors such as learning. Others are strapping tiny geolocator backpacks on the backs of migratory birds to probe their journeys and their mapping minds. They’re watching, tag- ging, measuring, conducting tireless observations, carefully preparing experiments at great length, some of which ultimately fail and must be reconfigured because their subjects are too wary or ornery. In short, these scientists are exploring the brains and behavior of birds in extraordinary, difficult—even heroic—ways.
But in this book, the birds themselves are the heroes of their own sto- ries. My hope is that by the time you finish these pages, the chickadee and the crow, the mockingbird and the sparrow, will look a little different to you. More like the bright fellow sojourners they are—enterprising, inventive, cunning, playful, shrewd individuals that sing to one another in “accents,” make complex navigational decisions without asking for di- rections, remember where they put things using landmarks and geome- try, steal money, steal food, and understand the mental state of another individual.
Clearly there’s more than one way to wire a clever brain.
Table of Contents
Introduction: The Genius of Birds 1
1 From Dodo to Crow: Taking the Measure of a Bird Mind 17
2 The Bird Way: The Avian Brain Revisited 39
3 Boffins: Technical Wizardry 63
4 Twitter: Social Savvy 101
5 Four Hundred Tongues: Vocal Virtuosity 137
6 The Bird Artist: Aesthetic Aptitude 171
7 A Mapping Mind: Spatial (and Temporal) Ingenuity 195
8 Sparrowville: Adaptive Genius 239