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Aesop’s fable had it right, crows are smart birds.

Remember it? The crow and the pitcher, a thirsty bird happens upon a vessel of water, but when he tries to drink from it, he finds the water level out of his reach. Not strong enough to knock over the pitcher, the bird drops pebbles into it — one at a time — until the water level rises enough for him to drink his fill.

UC Santa Barbara and Corina Logan and University of Auckland in New Zealand collaborators decided to put this to the test.

Their conclusion the birds’ intellectual prowess may be more fact than fiction. Her findings, supported by the National Geographic Society/Waitt Grants Program, appear today in the scientific journal PLOS ONE.

“We showed that crows can discriminate between different volumes of water and that they can pass a modified test that so far only 7- to 10-year-old children have been able to complete successfully. We provide the strongest evidence so far that the birds attend to cause-and-effect relationships by choosing options that displace more water.”

Getting the birds to respond and move in the right direction was the first hurdle.

“So I thought, let’s pretend the sky’s the limit and I can train them to do whatever I want,” Logan said. “I started by pointing at the one I wanted and continuing to point until he or she flew out. I got to the point where I could stand outside the aviary and point at the one I wanted and it would fly out while the other birds stayed put.”

“Two birds in particular — 007 and Kitty — became so well trained that Logan had only to call them by name and they’d fly into the testing room.”

“The testing room contained an apparatus consisting of two beakers of water, the same height, but one wide and the other narrow. The diameters of the lids were adjusted to be the same on each beaker. “The question is, can they distinguish between water volumes?” Logan said. “Do they understand that dropping a stone into a narrow tube will raise the water level more?”

“When we gave them only four objects, they could succeed only in one tube — the narrower one, because the water level would never get high enough in the wider tube; they were dropping all or most of the objects into the functional tube and getting the food reward,” Logan explained. “It wasn’t just that they preferred this tube, they appeared to know it was more functional.”

However, she noted, we still don’t know exactly how the crows think when solving this task. They may be imagining the effect of each stone drop before they do it, or they may be using some other cognitive mechanism. “More work is needed,” Logan said.

“What we do know is that one crow behaved like the older children, which allows us to explore how they solve this task in future experiments,” she continued. Research on causal cognition using the water displacement paradigm is only beginning to get at what these crows know about solving problems. This series of experiments shows that modifying previous experiments is useful for gaining a deeper understanding.

The research on the crows is part of a larger project Logan is working on to compare the cognitive powers of crows with those of grackles. “So far, no smaller-brained species have been tested with the tests we use on the crows, and grackles are smaller-brained,” she said. “But they’re really innovative. So they may have a reason to pay attention to causal information like this.”