Despite the fact that birds lack the brain structure called the cerebral cortex, which is used by mammals with advanced intelligence (think apes, elephants, dolphins and humans), both formal study and casual observation have shown time and again that corvids are among the most intelligent of animals.
There is the study that showed how a Eurasian corvid called a rook figured out that it could raise the level of water in a pitcher by adding rocks to it, just like in the ancient Aesop fable, so it could get a drink.
There is this video of a pair of hooded crows that take on a pair of fighting tomcats in a battle royal that clearly demonstrates the birds' intelligence.
And anyone who's ever watched crows or jays of any kind in their backyard has undoubtedly seen evidence of these birds' intelligence, whether it's stashing food for a later date or teaming up to mob and drive away hawks that show up in the neighborhood.
My most recent discovery of evidence of corvid intelligence is this video of some Russian ravens who are clearly playing in the snow just for the fun of it. Many animals play when they're young and it's considered a way of practicing skills that will be needed for survival in adulthood. When adult animals engage in play, however, it's generally considered a sign of higher intelligence.
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