domingo, 13 de abril de 2014

The Moral: Aesop Knew Something About Crows

ScienceTake: Those Clever Crows

Scientists are trying to understand the limits to the well-established intelligence of crows.

Crows and their relatives, like jays and rooks, are definitely in the gifted class when it comes to the kinds of cognitive puzzles that scientists cook up.

They recognize human faces. They make tools to suit a given problem.

Sometimes they seem, as humans like to say, almost human. But the last common ancestor of humans and crows lived perhaps 300 million years ago, and was almost certainly no intellectual giant.

So the higher levels of crow and primate intelligence evolved on separate tracks, but somehow reached some of the same destinations. And scientists are now asking what crows can’t do, as one way to understand how they learn and how their intelligence works.

One very useful tool for this research comes from an ancient Greek (or perhaps Ethiopian), the fabulist known as Aesop. One of his stories is about a thirsty crow that drops pebbles into a pitcher to raise the level of water high enough that it can get a drink.

Researchers have modified this task by adding a floating morsel of food to a tube with water and seeing which creatures solve the problem of using stones to raise the water enough to get the food. It can be used for a variety of species because it’s new to all of them. “No animal has a natural predisposition to drop stones to change water levels,” said Sarah Jelbert, a Ph.D. student at Auckland University in New Zealand, who works with crows.Photo
New Caledonian crows can use tools to solve problems, such as getting at hard to reach food.CreditMick Sibley

New Caledonian crows, rooks, Eurasian jays, and humans (past age 5) can do it, said Ms. Jelbert, who noted that great apes can do a slightly different version.

But in the latest experiment to test the crows, Ms. Jelbert, working with Alex Taylor and Russell Gray of Auckland and Lucy Cheke and Nicola Clayton of the University of Cambridge in England, found some clear limitations to what the crows can learn. And those limitations provide some hints to how they think.

The birds, Ms. Jelbert and her colleagues reported in PLOS One last month, were wild New Caledonian crows trapped for the experiment and then released.

The crows were first trained to pick up stones. This is not something they do in the wild. They then dropped the stones into a dry tube to gain a reward. Then they took the Aesop’s test, in several different situations.

The birds learned not to drop the stones in a tube of sand with a treat. And they correctly chose sinking objects rather than floating ones, and solid rather than hollow objects to drop in the water.

But if part of the tube apparatus was hidden, the birds could not learn. They also didn’t seem to be able to learn that the water would rise more quickly with fewer stones in a narrow tube.

This suggests two things, said Ms. Jelbert. They weren’t just learning abstract rules, because otherwise they would have been able to learn where to drop the stones to make the water rise even if they couldn’t see what was going on.

And second, the need to see the results of the behavior suggested they did seem to have “a level of causal understanding.” These are just hints, though, in terms of understanding how crows learn and think, said Ms. Jelbert, “we’re still very much at the beginning.”

April 10, 2014

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