Many associative neurons make crows intelligent
Size isn't everything: crows beat ostriches when it comes to neurons
Crows, birds from the same family as Brazilian grackles, are animals as intelligent as large primates—despite their tiny brains, which fit inside the bird's head and are about the size of a gorilla's thumb.
Like monkeys and chimpanzees, and much better than monkeys and even dogs, crows can recognize themselves in the mirror; they can distinguish quantities; and they not only use objects as tools, but also make their own tools with their beaks and claws.
How can animals with such small brains be capable of so much? When I was working in Brazil, my colleagues in the Czech Republic, who had easy access to various species of birds for research, discovered that songbirds, including parrots and crows, have numbers of neurons in their cerebral cortex comparable to those found in monkeys.
The finding is equivalent to discovering that a spoon and a soup plate contain similar numbers of seeds—which is only possible if the seeds in the spoon, like bird neurons, are much smaller than the seeds on the plate, like mammalian neurons. The more neurons, the greater the cortex's ability to process signals and information, we think.
But not all cortical neurons are the same: some process sensations and movements, while others connect things together, allowing the brain to create associations, find patterns, and invent rules. These are the associative neurons—and perhaps, in terms of cognitive flexibility, which is my definition of intelligence, this is what matters, much more than the total number of neurons.
To test this possibility, my group and two colleagues in Germany compared three species of crow with pigeons, chickens, and ostriches, the largest of the birds, with the largest brain. Once again, we saw that size isn't everything: although crows lose out to ostriches in terms of sensory neuron numbers, they win hands down in terms of associative neuron numbers, which we estimate to be as many as in the chimpanzee cortex. The study has just been published in the Journal of Comparative Neurology.
My next question now is how much energy it takes to operate so many neurons in brains of such different sizes: is it proportional to the number of neurons, the size of the brain, or something else? In other words, what determines how much energy a brain uses? Are birds more efficient than us primates in this regard?
I tried to address this issue when I was still working in Brazil, on a project in collaboration with the same researchers in Germany. They received eleven times the amount I was able to request from FAPERJ from the German government, and I never received it because the state of Rio de Janeiro went bankrupt. Fortunately for my research, I was able to move to another country, and how much energy a brain consumes is now a question I can answer. Stay tuned!