Until recently, if someone called you a bird brain, you knew they were calling you stupid! Everybody knew that birds operated off of instincts and were not capable of thought. Certainly, no one would think them capable of forethought, the ability to think into the future. This idea was fueled by the “unified theory of brain evolution” based on the work of Edinger more than 100 years ago. This concept was that the brains of animals evolved in a progressive and unilinear fashion, with humans at the pinnacle of this hierarchy. The brain and its complexity evolved from fish to amphibians to reptiles, then to birds and on to mammals, with primates and humans evolving to the highest level of ability for cognition.
Tracing Brain Development
In this simple model, there was an ordered chronology from lower to higher intelligence. The brains of these higher thinkers contained the more primitive structures found in “lower animals,” and the organization of these parts of the brain was similar. For example, the spinal cord of a fish is very close in its anatomical comparison to that of birds, mammals and even humans. The basic parts of the brain are also similar. This concept was fueled by embryology, as the development of the brains of embryos was similar. The brain of the bird, like that of mammals and reptiles, forms from a hollow tube of ectodermal tissue (the outer surface of the embryo) at the cephalic or head end of the embryo. This tube folds to form three divisions: the prosencephalon, which becomes the forebrain; the mesencephalon, which is the midbrain; and the rhombencephalon or hindbrain. The hindbrain and midbrain retain homologous structures among the motor and sensory nuclei and the reticular formation between mammals and birds.
However, it is the forebrain, which consists of the telencephalon and the diencephalon, that has followed a divergent line of evolution. This telencephalon develops on its outer surface — the cortex. This eight-layered outer surface of gray matter becomes the thinking cap of the brain, from directing actions, to knowing that we have been touched and where, to thinking about what we want to do tomorrow or 10 years from now. And the scientists “knew” that birds could not think because, well quite frankly, they did not have this outer cortex gray matter with its complex neural cells and circuitry. In fact, bird brains had an outer smooth surface, while human brains had this highly convoluted surface of gyri and sulci. So, it was reasoned that us humans, with our increased brain surface area, would be even bigger and better thinkers.
Edinger proposed that telencephalic evolution occurred in progressive stages of increasing complexity and size, culminating with the human cerebrum. He proposed that, first, there was the old brain, the paleoencephalon (also called the basal ganglia or subpallium at the telencephalic base), which controlled instinctive behavior. This was followed by the addition of a new brain, the neoencephalon (also called the pallium or mantle at the top of the telecephalon — that eight-layered cortex of gray matter), which controlled learned and intelligent behavior. So birds, he reasoned, really were not that smart as they had none of those outer cortex cells of gray matter to think with – which gave them the rightful title of bird brains!
Delving Deeper Into Bird Brains
Scientists continued to study tracts and brain function in birds and other animals in the 1970s up to the present using new techniques. Based on tract tracing and receptor studies, scientists learned that the hookups were similar but at a deeper level in the brain between mammals and birds. And even more exciting, the functions were similar! For example, functional studies revealed that both the mammalian neostriatum and the avian paleostriatum augmentatum (deeper inside the brain) participate not only in instinctive behavior and movement, but also in motor learning. So more and more evidence was accumulating that birds do, in fact, think.
As this information was accumulating in many aspects of brain function, a group of scientists decided that all of the names had to change to reflect new concepts of brain connectivity and brain function for birds. This Avian Brain Nomenclature Consortium met and since then has been continually revising the names for the parts of the brains of birds. Their premise was that to move forward, the names of the components of brains of birds had to reflect the functions and homologies with those of mammals.
The Crow Knows …
This modern view, with its understanding that the pallium comprises about 75% of the telencephalic volume in the bird and that it processes sensory and motor cortices of the bird similar to mammals, opens up new avenues of understanding of the cognitive abilities of birds. Data from pigeons show that they are able to discriminate up to 725 visual patterns, understand the concept of human made vs natural made, communicate with visual symbols, and the list continues. Crows are able to do some extraordinary tasks – making tools and retrieving objects, figuring out complex tasks, and teaching other crows. There have been studies that show that crows that have been caught by people wearing masks will somehow transmit that information to other crows outside of that flock population. The people with masks will then be harassed by these new crows. Our parrot friends – we know just by living with them – discriminate between people, display tool making and manipulation and have vocal learning. Some parrots, like African greys, have the uncanny ability to tell us concepts in sentences at appropriate times. And we marvel at them – and we should! Because to be called a birdbrain now in the 21st century … well, that is very special!