New Caledonian crows are known for using tools in the wild. A team is investigating the cognitive abilities of these crows, which live on the archipelago of New Caledonia in the southwest Pacific Ocean, 750 miles (1,200 kilometers) east of Australia.
It was there, on the island of Grand Terre, that Sarah Jelbert, a doctoral student at Auckland University in New Zealand, and her colleagues tested the crows' understanding of cause and effect by presenting them with a test straight out of Aesop's Fables.
In one fable, "The Crow and the Pitcher," a thirsty crow can't reach the water at the bottom of a pitcher, but then begins to drop one pebble after another into the vessel. Slowly, the water rises to the top, and the bird gets its drink. How did Jelbert's New Caledonian crows measure up when presented with a similar test?
The scientists recently published their results in PLOS One. National Geographic caught up with Jelbert by phone to ask her more about the study and these smart birds. (See "Crows Have Human-Like Intelligence, Author Says.")
Why did you choose to work with New Caledonian crows?
They make tools in the wild, something that very few animal species do. They make tools out of sticks and shape them with their beaks to form a hook on the end. And then they use their sticks to lever grubs out of holes in rotting logs.
The grubs are fat and gel-like, so if they just poked a stick into them, they'd end up popping them and would have only a horrible mush of grub. But by using the hook on the end of their stick, they can lift them out.
We actually have a go at this ourselves at times. We have to collect the grubs for our work; we use them to catch the crows. Most of the grubs are inside the logs, and we have to hack them out with machetes. It's one of the more disgusting parts of the job. (See "Crows Better at Tool Building Than Chimps.")
The birds also make a tool from Pandanus leaves; it's a small bush that grows something like a palm. They use their beaks to snip into the side of a leaf, and then rip it up about 10 to 15 centimeters [4 to 6 inches], and snip it off at the top. The Pandanus leaves have natural barbs on their edges, so they make great tools. The birds use them to drag out insects that live beneath leaf litter.
What else can the crows do that surprises people?
We're still getting our heads around all they can do. One interesting thing: They don't use their tools just to get food, but [also] to investigate things they find that are scary, like a plastic snake in a box. They'll poke it first with a stick to see if it is dangerous.
What's your experimental setup like? You're working with wild crows?
Yes. We have a large aviary on Grande Terre. We set up nets in the wild, and will catch 6 to 12 birds, and bring them back to the aviary where they're nicely fed and cared for. We keep them for three months, and then return them to the wild so they can carry on with their lives.
How did you come up with your idea to give the Aesop's Fable test to the crows?
Our study was based on the fantastic work of two other researchers, Christopher Bird and Nathan Emery. [They showed that rooks would use stones to raise the water level in a tube so that they could reach a worm.] Dropping stones into water isn't something New Caledonian crows do in the wild; no animal does. But it is also a completely natural thing, and so is a fair test of animals' cognition.
We trained six crows to drop small stones into tubes. And then we gave them different tests to see how much they understand or can learn about the cause and effect of water displacement. Would they understand that dropping stones into water in a tube [to get a piece of meat to float to the top] is different from dropping them into sand in a tube? Or that hollow objects have a different effect from solid ones?
They did very well at four of the six tests, where they were able to apply their natural understanding of cause and effect and the properties of objects. They understood that solid objects sink and hollow ones float, for instance, and that it doesn't make any sense to drop stones into sand. But they were incredibly poor at the counterintuitive test, which involved a U-[shaped] tube; they had to infer that there was a connection between the two tubes, but none of them could do this.
And what do their successes and failures at these tests tell us about the cognitive abilities of New Caledonian crows?
We're trying to understand the cognitive mechanisms of animal minds, and to do that you need to look at tests that animals can pass and those that they fail. In human psychology, researchers have discovered that the way people make mistakes is often most informative about how they think. The errors give away how they are solving problems. Is this true for animals, too? Or do they have a completely different way of conceptualizing problems? By looking at the errors the crows make, we may get a better understanding of how they successfully solve problems.
Are the New Caledonian crows that you've used in your experiments putting what they've learned in your aviary to use in the wild?
Well, I hope so [laughs]. But we normally don't see them again after we set them free. We go to new areas to catch new birds.