It’s a general rule in neuroscience that the smaller the brain, the smaller the cognitive function. But scientists at Charles University in Prague have proven how some species of birds buck the trend.
In particular parrots and corvids (such as crows, ravens, and magpies) have long shown signs of superior intellect. They have the ability to manufacture and use tools, solve problems, recognise themselves in a mirror and even plan for the future.
And if you thought “Polly wants a cracker” was impressive, you were right. Vocal learning is a rare talent in the animal kingdom that allows parrots, corvids and other songbirds to recognise and mimic human language.
So how do they pack all these capacities into a brain weighing less than 25 grams? As explained in their Proceedings of the National Academy of Sciences paper, researchers looked at 28 species of birds with the help of an isotropic fractionator (a neuron counting device) that was able to determine the number of neurons in different regions of the animals’ brains.
What they found is that our feathered friends have a very high number of neurons packed in with a density that in parrots and songbirds means they can “accommodate about twice as many neurons as primate brains of the same mass and two to four times more neurons than rodent brains of equivalent mass”.
For example, cockatoos have two billion neurons in their brains that weigh just 10 grams, twice as many as a marmoset monkey with a brain of the same size. Similarly, the brain of a raven weighs 10.2 grams and is packed with 1.2 billion neurons, fractionally more than the number a capuchin monkey's brain has, despite it weighing four times as much.
This results in the birds' brains having the potential for “much higher cognitive power per unit mass” than those of their mammal counterparts. Even though the connection between intelligence and neuron count hasn't been firmly established, this study does show there are other ways to make for a smarter brain than just sheer size.
“This pretty much answers the question we began with: how can these birds be so clever with such small brains?” study co-author Pavel Němec told The Guardian. “The answer is that there are so many neurons, their computing power is comparable to that of primates.”