THE NEW CALEDONIAN crow is surprisingly smart about its food. Its favorite insects live in tiny crevices that are too narrow for its beak. So the crow takes a barbed leaf and, using its beak and claws, fashions a primitive hook. It then lowers the hook down into the cracks, almost like a man fishing, and draws up a rich meal. Some scientists even suggest that crows are more sophisticated tool builders than chimps, since they can transmit their knowledge on to successive generations and improve the tools over time. These birds have a culture.
The world lost its most famous bird brain this month: Alex, an African gray parrot who lived in a Brandeis laboratory and possessed a vocabulary of nearly 150 words. Yet as remarkable as Alex was - he could identify colors and shapes - he was not alone. The songs of starlings display a sophisticated grammar once thought the sole domain of human thinking. A nutcracker can remember the precise location of hundreds of different food storage spots. And crows in Japan have learned how to get people to crack walnuts for them: They drop them near busy intersections, then retrieve the smashed nuts when the traffic light turns red.
These feats are part of a growing recognition of the genius of birds. Scientists are now studying various birds to explore everything from spatial memory to the grammatical structure of human language. This research is helping to reveal the secrets of the human brain. But it is also overturning the conventional evolutionary story of intelligence, in which all paths lead to the creation of the human cortex. The tree of life, scientists are discovering, has numerous branches of brilliance.
"It used to be that people would only talk about intelligence in terms of primates," says Nicola Clayton, a professor of comparative psychology at the University of Cambridge. "But now I think that birds have achieved a sort of honorary ape status, just with a few feathers attached."
The intelligence of birds, which sit far from man on the evolutionary tree, has also forced a reappraisal of where intelligence comes from. Scientists once assumed that intelligence evolved out of physical need - animals got smart in order to exploit natural resources. But the brainpower of birds suggests that intelligence is actually a byproduct of complex social interactions. Living in a group requires an animal to juggle lots of information about its peers. So it's not a coincidence that the smartest creatures are also the most social.
Crows, for example, live in strikingly human social structures. They are devoted to their families, but can assemble in much larger flocks if resources are sufficient. African grays follow a similar pattern, roosting at night with hundreds of other birds, but foraging during the day with an intimate group of kin. These intricate social structures mean that many birds are subject to the same social challenges as primates. It is these challenges, the research suggests, that make them so smart.
. . .
For most of the 20th century, "bird brain" has been used as an insult. Noting the stark structural differences between human and bird brains, anatomists concluded that birds are essentially flying reptiles. Their minds were too tiny for thought. But in recent years, scientists have discovered that the bird brain doesn't deserve its reputation.
In 2005, Alex wowed many scientists when he began spontaneously using the word "none" to represent a rudimentary conception of zero. He also enjoyed inventing new words for things: he referred to almonds as "cork nuts," since the texture of the nut resembles that of a wine cork. An apple was a "banerry," a combination of two of his favorite other fruits, bananas and cherries.
"All of these cognitive abilities weren't supposed to be possible in birds," says Dr. Irene Pepperberg, the scientist who worked with Alex. "But Alex showed us just what a bird brain is capable of."
The first aspect of bird intelligence scientists studied was birdsong. Charles Darwin compared the early vocalizations of young songbirds with the babbling of human infants, noting that both species went through a period of intense vocal learning. In the early 1970s, Fernando Nottebohm, a neuroscientist at Rockefeller University, wanted to understand how certain songbirds managed to learn new melodies every year. As Nottebohm notes, birds are the only other species that "attempts vocally to do anything like what we do." Perhaps, he wondered, the impressive learning abilities of songbirds could be used to understand aspects of the human mind.
Nottebohm's search for the source of birdsong led him to discover something entirely unexpected. In order for birds to learn new songs, they have to generate new brain cells. At the time, this was a radical idea. Neuroscientists believed that virtually all animal brains - and certainly the human brain - stopped creating new brain cells shortly after birth. But Nottebohm showed that up to 1 percent of the neurons in the song center of their brains were created anew, every day.
Other researchers, including Elizabeth Gould of Princeton, later extended Nottebohm's data to a long list of other species, including great apes and humans. The research that began with a canary's melody is now being used to help develop potential treatments for a wide range of human illnesses, from Parkinson's disease to spinal cord injuries.
"These little birds overturned one of the big dogmas of neuroscience," Nottebohm says.
Timothy Gentner, a neuroscientist at the University of California at San Diego, is using European starlings to overturn another deeply held scientific idea: that only humans are capable of learning complex grammatical patterns. According to research published last year in the scientific journal Nature, songbirds can be trained to distinguish a system of "warbles" and "rattles" that share the same underlying structure as a human sentence. Some saw the surprising results as a refutation of the position, advanced by scientists such as Noam Chomsky, that the human mind is uniquely designed to deal with such grammar.
While Chomsky dismissed the study as having "nothing to do with language," Gentner believes that starlings reveal "the deep biological roots of human language."
The grammatical skills of male songbirds are driven by their elaborate social interactions with females. "The goal of a singing starling is to find a mate," Gentner says. "They make their songs more and more complex in order to impress the females. The ability to learn these grammatical patterns grew out of that. It's like a cognitive version of the peacock's tail."
Similar social pressures have driven other aspects of avian intelligence. Many birds store vast quantities of food in various hiding spots, which they later recover when food is scarce. (Clark's nutcracker, for example, is able to store more than 30,000 seeds in hundreds of hiding spots over a 12-square-mile area. No primate can match this.) The problem with stored food, however, is that it's easy to steal. As a result, many birds regularly re-hide their food if they suspect other birds have observed their original spots.
This suspicious behavior depends on a very impressive feat of social intelligence, which had never before been observed outside primates. Nicola Clayton and Nathan Emery, another researcher at the University of Cambridge, showed in 2001 that only western scrub jays that had previously stolen food from other birds would always re-hide their food. Jays that had never stolen before didn't worry about being stolen from.
"These birds are projecting their experience of being a thief onto other birds," Clayton says. "They are thinking 'Well, I've stolen food, so this guy might too.' It's a form of mental simulation."
Such cognitive skills require a big brain. In fact, the brains of crows and some parrots are roughly the same size as the chimpanzee brain relative to body size. These avian brains are also enlarged in areas that approximate the primate prefrontal cortex, a region that underwent a great expansion during human evolution.
But these broad similarities are the exception to the rule. For the most part, the clustered anatomy of the bird brain is organized very differently from the layered anatomy of the primate brain. For scientists, that's part of what makes the bird brain so fascinating. It's a different anatomical solution to the same evolutionary problem of how to live as a social species.
This suggests that some rarefied aspects of human intelligence, such as tool use and the ability to imagine what other minds are thinking, have actually evolved independently in birds. In the history of life, the primate brain and bird brain diverged hundreds of millions of years ago; birds are direct descendants of dinosaurs. Yet the unfolding research into avian intelligence shows that humans have much to learn from birds. Among the lessons: that we, like birds, are smart because we have to deal with each other.
Jonah Lehrer is an editor at large at Seed magazine. His first book, "Proust Was a Neuroscientist," will be published in November.