Why are crows so smart?
The intelligence of these brainiest of birds has been compared to that of a seven-year-old human. Belinda Smith delves into the behavioural neuroscience behind crow cognition.
They can recognise faces, use tools – even drop nuts on a road for cars to crack (then pick them up with the safety of pedestrian lights).
Birds in the corvid family – most famously, crows – are known for their intelligence. Even ancient Greek storyteller Aesop wove their problem-solving nouse into his famed fables. But why are they so smart?
Well, first up: not all crows are super smart. There are around 40 species of crows and ravens from a family of more than 120 corvids. "There's a fair bit of disparity between crow species," says Matt Brown, a PhD student in crow cognition at Griffith University in Queensland, Australia.
The New Caledonian crow is, so far, the most intelligent of its crow brethren, Brown says: "They're to crows what we are to the rest of the primates."
Proficient toolmakers, New Caledonian crows use sticks and serrated palm fronds to dig out insects from inside trees. A 2014 study published in Learning and Behavior showed them using a range different tools across different sites on the island.
But other members of the corvid family are also pretty brainy. Emulating Aesop's The Crow and the Pitcher, a famous 2009 study in Current Biology showed rooks, a corvid that doesn't seem to use tools in the wild, dropping stones in water, gradually raising the level until they could reach a tasty floating worm.
And corvids don't even need instructions to get a job done. A 2014 Current Biology study showed they can work problems out spontaneously.
So what's going on?
Crows tend to have big brains compared to their body size, Brown says. In mammals, the bigger-brained are humans and dolphins; in birds, it's parrots and crows.
And getting into the neuroscientific nitty gritty of it all, the part of the brain responsible for crow smarts is the "nidopallium caudolaterale". Two studies published in the Proceedings of the National Academy of Sciences last year showed just what the nidopallium caudolaterale can do.
Andreas Nieder's laboratory from Germany's University of Tübingen recorded signals from individual neurons in crow brains. One of their studies found neurons in the nidopallium caudolaterale change during a learning task, while in another crows were presented with varying numbers of objects, such as four dots. Neurons in their nidopallium caudolaterale seemed to be "tuned" to different numbers.
In mammals, the equivalent brain area is the prefrontal cortex, which is responsible for executive functions such as social behaviour and decision making.
Surely, in the wild, a crow doesn't need to know how to count.
(The nidopallium and prefrontal cortex are examples of convergent evolution: some 300 million years ago, birds and mammals split, long before any sophisticated brain structures such as the nidopallium existed. And over time, they evolved independently.)
So why this incredible bird brainpower? Surely, in the wild, a crow doesn't need to know how to count. And the brain's a fuel-guzzler, so any increase in size needs to be worth the extra energy.
While no one knows for sure, Brown says, the leading theory is what's called the social intelligence hypothesis.
Chimpanzees, for instance, have their own brand of politics, where not only do they have to keep tabs on their own relationships, but also those between others. That "social intelligence" needs a lot of brain power.
Many species of crow pair off as adults and become sedentary but territorial mates for life. Interactions with other crows are minimal.
But growing up is a different story. During younger years, they often live in larger flocks dubbed juvenile gangs. "It's exactly how it sounds: they're basically a bunch of teenagers trying to compete with each other," Brown says. And it's these relationships they have to keep tabs on.
A side effect of this is they can also keep tracks of their relationships with people. So the next time you shoo away a crow, remember: it's making a mental note of the experience and may one day get its revenge.