Alex Taylor et al

Caledonian crows are famed for their smarts. They have been known to properly interpret reflections to find food and their ability to make and use tools rivals chimpanzees for sophistication.

But these brainy birds have been beaten in a recent intelligence test by a bunch of babies. It's a rare failure, but it appears they are unable to interpret cause and effect to create new solutions without direct experience of the events.


If you observed a brick falling onto a button that dispensed food, you would quickly realise that you didn't need the brick to get the food. You could just push the button yourself.

You have observed a sequence of cause and effect, and although you haven't directly experienced it, you can figure out what's going on and get the food.

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Caledonian crows, according to a new study published in Proceedings of the Royal Society B: Biological Sciences, aren't able to do this.

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"The crows are great at solving certain types of problems but, as our new study shows, struggle at others," lead author Alex Taylor told Wired.co.uk via email. "Discovering the limits of their cognition allows us to get a better understanding of how intelligence evolves, and which aspects our our cognition are particularly special."

Taylor and his colleagues have studied Caledonian crows for years, and have been the source of numerous papers on their intelligence, including a March paper that replicated Aesop's Fable of a thirsty crow using stones to raise the water level in a half-filled container.

Indeed a 2009 study showed that the crows are able to understand cause and effect quite well. Crows that received food as an effect of pushing a platform with their beak then learned to use other tools, like stones, to move the platform if it was out of reach.

The crucial difference, said Taylor, is that this required a direct experience. The crows had previously pushed the platform themselves. "Animals are very good at learning from their own experience, or via observing the effects of others (social learning)," he said. "But so far only humans appear to be able to simply observe an effect in the world, and, without reference to their own behaviour or another humans, then create a novel behaviour to cause the effect."

To test this hypothesis, Taylor set up an experiment where a block sat above a rotating cylinder. If the block fell on to the cylinder, a portion of meat would become available to the crows.

Initially, the block itself was baited with meat. If the crow tried to grab the meat, the block would fall, turning the cylinder and making a different portion of meat available as a reward.

But then an unbaited block was placed beside the cylinder. All the crows had to do in order to get the prize of meat was to pick it up and drop it on the cylinder. Despite having observed the block turning the cylinder previously they were unable to complete the task as it required them to do something different than before.


A group of two-year-old human babies, on the other hand, were able to solve the problem with ease. The same experiment was repeated with a marble instead of meat. On the first try, a baited block was placed above the cylinder. When the baby tried to grab it, the block would fall, the cylinder would turn and then a second marble would become available.

When an unbaited block was placed beside the cylinder, the babies figured out that they could just pick it up and drop it on the cylinder in order to get a marble. "The key issue here is understanding causality via observation alone, rather than experience," said Taylor. "Humans can observe an effect of the wind blowing, such as causing fruit to fall from a tree, and then create behaviour to recreate the same effect, such as shaking the branch (or see a domino hit a stone, and the pick up the stone and drop it to create the same effect)." "This behavioural freedom may be one of our most under-appreciated cognitive abilities," he added.

Despite their wits, it seems like this round is Caledonian crows zero, human babies one. In your face, nature.