Well, we say ‘Einsteins’ – maybe that’s overestimating their intelligence, but it has been proven that they have the reasoning abilities of a five to seven-year-old child.

New studies conducted by California-based research facility Plos One used a test based on one of Aesop’s fables, in which a clever crow works out he can raise water levels by dropping stones into a container.

The New Caledonian crows were given a similar task – they were shown cylindrical containers filled with water, with food floating on the top.

Not only did they work out how to get to the food by adding stones, they also chose containers with higher water levels and added solid, not hollow, objects – so they completed the task as efficiently as possible.

However, they were stumped when it came to containers with a u-shaped bend.

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