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.
The "bird brain" was seen as less complex by the comparative anatomists of 100 years ago, whose techniques were centered on observing the characteristics of whole brains from deceased subjects. (I remember seeing a display of pickled whole brains at Cornell University, human brains from a variety of subjects including scientists and notorious criminals. You had to read the tags carefully to determine if you were looking at a "good brain" or "bad brain".) German neurobiologist Ludwig Edinger, known as the father of comparative anatomy, compared the brains of all kinds of vertebrates, noting similarities and differences.
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.
Scholars of bird behavior have long known that birds can do things that cannot be attributed to instinct alone. Crows and ravens make tools, parrots not only mimic words, but can rearrange them to convey new thoughts. I know that mother killdeer will fake a broken wing to lure intruders away from a nest, but they still fool me half the time. I admit that the domestic chicken is not the smartest bird around, but when you watch a mother hen raising chicks and communicating with a variety of vocalizations, you start to wonder if chickens are only dumb because we raise them dumb.
Scientist now agree that the bird brain is not just a replica of the basest part of the mammalian brain, but that it has upper and base sections, also. They agree that the upper section of the bird brain is organized into clusters, as opposed to the six layers of upper brain organiztion im mammals. There are competing ideas on how the clusters evolved or exactly how they might be analagous to mammalian brain structure.
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.
We can look forward to more findings and an interesting new line of research.