Mar. 26 study in PLOS ONE that tested what researchers call the "Aesop's Fable Paradigm."
In the ancient Greek tale "The Crow and the Pitcher," a parched crow
came upon a water pitcher that was partially full, but couldn't fit its
beak far enough inside to reach the water. So the crow gathered pebbles
and dropped them into the pitcher, raising the water level so it could
quench its thirst — and showing an impressive understanding of the cause
and effect of water displacement in the process.
Apparently, this wasn't too far fetched.
Crows, rooks, and jays, or Corvidae, top the avian I.Q. scale (sorry, owls); and studies have previously shown that they can indeed learn to raise the water level in a glass in order to snack on a floating worm.
A group of researchers decided to test the extent of these cognitive
abilities by studying a clever species of crow native to the Pacific
island of New Caledonia.
They wanted to see whether the crows could understand causal
relationships — namely, the idea that if you drop objects in water, it
raises the level of the water — and to compare the crows' results to
those of children who had previously figured out similar puzzles.
So they caught six birds and devised six experiments, three of which
had previously been done by children. Each task involved trying to raise
the water level in a tube enough that the crow could grab the reward of
a small scrap of meat tied to a cork.
As crows don't generally drop rocks in the wild — thankfully for the
rest of us — the researchers trained them to pick up rocks and drop them
into tubes. This was to get the birds used to the idea of using rocks
as a tool (these birds are known to make and use tools). When children
did the same experiment in 2012, they received similar training. Though
the kids had only 5 trials for each experiment, the crows got 20 chances
to see if they could successfully learn to solve each task.