Crows can solve some puzzles just about as well as 5 to 7-year-old children, found a 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.

Here's what happened.

Experiment 1

The first test the crows faced presented them with two tubes. One contained water and a reward; the other contained sand and a reward. The researchers wanted to see if the crows could figure out that dropping rocks into the water tube would put the reward within reach, while doing the same to the sand tube would do nothing.

This was an easy one — all six birds dropped significantly more stones into the water tube. Five of the birds learned the system within 15 tries. The sixth bird, named R, took the full 20 trials to approach statistically significant results, meaning the researchers thought there was a 1% possibility that he passed the trial due to chance.

Experiment 2





In experiment 2, crows chose between heavy and light objects to drop into the water - the light objects were light enough to float. They opted for heavy, sinking objects 88% of the time. The bird called R picked up the light objects 16 times, but never dropped one in the water. After this trial he quit, due to what the researchers describe as "lack of motivation."

Experiment 3

Experiment three was the first time New Caledonian crows had ever been tested on whether they would choose solid objects over hollow objects. They consistently did so, picking the solid object, which would raise the water level higher, 89% of the time.

Experiment 4





Task 4 was the worst performance for the crows all day. One of these tubes is much narrower than the other. Dropping objects into the narrower tube would be more efficient and a quicker way to get a snack then using the wider tube. Yet the crows chose the narrow tube only 39% of the time.

Still, this test was not quite like the others.

The researchers designed it so that birds could get the reward from either tube. Most of the time, the birds simply picked one and kept dropping objects into it until they got the piece of meat. They say that this could mean there was "insufficient motivation" to learn the right strategy, though they think that this is unlikely. More likely, they say, is that the crows understand the tools they are using, but perhaps don't understand the properties of the water they are using the tools on quite as well.

After this trial, another crow, WG, declined to participate anymore and joined R in the "lack of motivation" group.

Experiment 5

Task 5 presented the remaining crows with options similar to task 4 — narrow and wide tubes — but this time, the narrow tube had too little water in it to make it possible to get the reward.

Interestingly, although all birds tried the narrow tube the first time around, they learned to avoid it. In in end they made the correct choice and opted for the wide tube 86.8% of the time.

Experiment 6

The last test presented the crows with an additional complication. The reward was in a tube they couldn't fit a rock into, and only one of the other two outside tubes was connected to the middle one. They couldn't see the connection. The birds were puzzled by this task, and chose the right tube only 48.9% of the time, a result no better than chance.

What This All Means

In 2012, groups of children completed experiments 1, 2, and 6. On experiments 1 and 2, the 5 to 7-year-old group performed similarly to the crows, showing that they were able to learn how to get a reward in the same way. As for experiment 6, called the "u-tube" trial, the kids were able to eventually learn how to get their reward, unlike the crows, even though most kids also had trouble understanding how the tubes were connected. Instead, the kids more frequently just dropped a stone into a tube, and if it worked, kept on choosing that tube. This was a way to pass the task, but without understanding the causal relationship researchers were looking for.

According to the researchers, passing four out of six tasks shows that the New Caledonian crows have at least a basic ability to understand or learn cause and effect relationships, similar to 5 to 7-year-olds. That's pretty impressive for animal cognition. But this research also shows some of the birds' limits, especially when they face unseen obstacles. And it also seems that some crows have issues with motivation.

Even though the crows couldn't solve all the puzzles, the researchers don't want to give up hope that some other crows could do better. "As only a small number of birds took part in this study, we cannot assume this reflects a species-wide failure," they wrote.

Here's the video:

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Video by Sarah Jelbert