Birdbrain has long been a colloquial term of ridicule. The common notion is that birds' brains are simple, or so scientists thought and taught for many years. But that notion has increasingly been called into question as crows and parrots, among other birds, have shown what appears to be behavior as intelligent as that of chimpanzees.
The clash of simple brain and complex behavior has led some neuroscientists to create a new map of the avian brain.
Today, in the journal Nature Neuroscience Reviews, an international group of avian experts is issuing what amounts to a manifesto. Nearly everything written in anatomy textbooks about the brains of birds is wrong, they say. The avian brain is as complex, flexible and inventive as any mammalian brain, they argue, and it is time to adopt a more accurate nomenclature that reflects a new understanding of the anatomies of bird and mammal brains.
''Names have a powerful influence on the experiments we do and the way we think,'' said Dr. Erich D. Jarvis, a neuroscientist at Duke University and a leader of the Avian Brain Nomenclature Consortium. ''Old terminology has hindered scientific progress.''
The consortium of 29 scientists from six countries met for seven years to develop new, more accurate names for structures in both avian and mammalian brains. For example, the bird's seat of intelligence or its higher brain is now termed the pallium.
''The correction of terms is a great advance,'' said Dr. Jon Kaas, a leading expert in neuroanatomy at Vanderbilt University in Nashville who did not participate in the consortium. ''It's hard to get scientists to agree about anything.''
Scientists have come to agree that birds are indeed smart, but those who study avian intelligence differ on how birds got that way. Experts, including those in the consortium, are split into two warring camps. One holds that birds' brains make the same kinds of internal connections as do mammalian brains and that intelligence in both groups arises from these connections. The other holds that bird intelligence evolved through expanding an old part of the mammal brain and using it in new ways, and it questions how developed that intelligence is.
''There are still puzzles to be solved,'' said Dr. Peter Marler, a leading authority on bird behavior at the University of California, Davis, who is not part of the consortium. But the realization that one can study mammal brains by using bird brains, he said, ''is a revolution.''
''I think that birds are going to replace the white rat as the favored subject for studying functional neuroanatomy,'' he added.
The reanalysis of avian brains gives new credibility to many behaviors that seem odd coming from presumably dumb birds. Crows not only make hooks and spears of small sticks to carry on foraging expeditions, some have learned to put walnuts on roads for cars to crack. African gray parrots not only talk, they have a sense of humor and make up new words. Baby songbirds babble like human infants, using the left sides of their brains.
Avian brains got their bad reputation a century ago from the German neurobiologist Ludwig Edinger, known as the father of comparative anatomy. Edinger believed that evolution was linear, Dr. Jarvis said. Brains evolved like geologic strata. Layer upon layer, the brains evolved from old to new, from fish to amphibians to reptiles to birds to mammals. By Edinger's standards, fish were the least intelligent. Humans, created in God's image, were the most intelligent. Edinger cut up all kinds of vertebrate brains, noting similarities and differences, Dr. Jarvis said.
In mammals, the bottom third of the brain contained neurons organized in clusters. The top two-thirds of the brain, called the neocortex, consisted of a flat sheet of cells with six layers. This new brain, the seat of higher intelligence, lay over the old brain, the seat of instinctual behaviors.
In humans, the neocortex grew so immense that it was forced to assume folds and fissures, so as to fit inside the skull.
Birds' brains, in contrast, were composed entirely of clusters. Edinger concluded that without a six-layered cortex, birds could not possibly be intelligent. Rather, their brains were fully dedicated to instinctual behaviors.
This view persisted through the 20th century and is still found in most biology textbooks, said Dr. Harvey Karten, a neuroscientist at the University of California, San Diego, and a member of the consortium, whose research has long challenged the classic view.
There is a bird way and a mammal way to create intelligence, Dr. Karten said. One uses clusters. One uses flat sheet cells in six layers. Each exploits the basic design of having a lower brain and a higher brain with mutual connections.
In the 1960's, Dr. Karten carried out experiments using new techniques to trace brain wiring and identify the paths taken by various brain chemicals. In humans, a chemical called dopamine is found mostly in lower brain areas, called basal ganglia, which consist of clusters.
Using the same tracing techniques in birds, Dr. Karten found that dopamine also projected primarily to lower clusters and no higher. Later studies show numerous similarities between clusters in the mammalian brain and lower clusters in the avian brain. Experts now agree that the two regions are evolutionarily older structures that lie underneath a newer mantle.
Where the experts divide is on the question of the upper clusters in a bird's brain. Agreed, they are not primitive basal ganglia. But where did they come from? How did they evolve? What is their function?
Dr. Karten and others in the consortium think these clusters are directly analogous to layers in the mammalian brain. They migrate from similar embryonic precursors and perform the same functions.
For example, in mammals, sensory information -- sights, sounds, touch -- flows through a lower brain region called the thalamus and enters the cortex at the fourth layer in the six-layered cortex.
In birds, sensory information flows through the thalamus and enters specific clusters that are functionally equivalent to the fourth layer. In this view, other clusters perform functions done by different layers in the mammal brain.
A second group, including Dr. Georg Striedter of the University of California, Irvine, a consortium member, believes that upper clusters in the avian brain are an elaboration of two mammalian structures -- the claustrum and the amygdala. In this view, these structures look alike in bird and mammal embryos. But in birds they grow to enormous proportions and have evolved entirely new ways to support intelligence.
In mammals, the amygdala is involved in emotional systems, Dr. Striedter said. ''But birds use it for integrating information,'' he said. ''It's not emotional anymore.''
Meanwhile, examples of brilliance in birds continue to flow from fields and laboratories worldwide.
Dr. Nathan Emery and Dr. Nicola Clayton at the University of Cambridge in England study comparisons between apes and corvids -- crows, jays, ravens and jackdaws. Relative to its body size, the crow brain is the same size as the chimpanzee brain.
Everyone knows apes use simple tools like twigs, Dr. Emery said, selecting different ones for different purposes. But New Caledonian crows create more complex tools with their beaks and feet. They trim and sculpture twigs to fashion hooks for fetching food. They make spears out of barbed leaves, probing under leaf detritus for prey.
In a laboratory, when a crow named Betty was given metal wires of various lengths and a four-inch vertical pipe with food at the bottom, she chose a four-inch wire, made a hook and retrieved the food.
Apes and corvids are highly social. One explanation for intelligence is that it evolved to process and use social information -- who is allied with whom, who is related to whom and how to use this information for deception. They also remember.
Clark nutcrackers can hide up to 30,000 seeds and recover them up to six months later.
Nutcrackers also hide and steal. If they see another bird watching them as they cache food, they return later, alone, to hide the food again. Some scientists believe this shows a rudimentary theory of mind -- understanding that another bird has intentions and beliefs.
Magpies, at an earlier age than any other creature tested, develop an understanding of the fact that when an object disappears behind a curtain, it has not vanished.
At a university campus in Japan, carrion crows line up patiently at the curb waiting for a traffic light to turn red. When cars stop, they hop into the crosswalk, place walnuts from nearby trees onto the road and hop back to the curb. After the light changes and cars run over the nuts, the crows wait until it is safe and hop back out for the food.
Pigeons can memorize up to 725 different visual patterns, and are capable of what looks like deception. Pigeons will pretend to have found a food source, lead other birds to it and then sneak back to the true source.
Parrots, some researchers report, can converse with humans, invent syntax and teach other parrots what they know. Researchers have claimed that Alex, an African gray, can grasp important aspects of number, color concepts, the difference between presence and absence, and physical properties of objects like their shapes and materials. He can sound out letters the same way a child does.
Like mammals, some birds are naturally smarter than others, Dr. Jarvis said. But given their range of behaviors, birds are extraordinarily flexible in their intelligence quotients. ''They're right up there with hominids,'' he said.