By Rebecca Morelle
Science reporter, BBC News
Crows have shown that two tools are better than one when it comes to problem solving, scientists say.
A University of Auckland study has revealed that New Caledonian crows can use separate tools in quick succession to retrieve an out-of-reach snack.
The birds were using reasoning that was more commonly seen in great apes and humans, the New Zealand team reported in the journal Current Biology.
New Caledonian crows are renowned for their tool-making ability.
The birds (Corvus moneduloides), which are found on the South Pacific island of New Caledonia, use their bills to whittle twigs into hooks and cut and tear leaves into barbed probes that can extract bugs and grubs from crevices.
To further test the crows' tool-using talents, scientists set seven wild birds a tricky task.
The crows were presented with:
- A scrap of meat, which was tucked away, out of reach, in a box;
- A small twig, which was too short to reach the food;
- And another longer twig, which was long enough to reach the food, but was locked away well out of bill-grabbing range in another box.
The birds surprised the scientists with their quick thinking.
Alex Taylor, lead author of the paper, said: "The creative thing the crows did was to use the short stick to get the long tool out of the box so that they could then use the long stick to get the meat."
Russell Gray, another author of the paper, told the BBC News website: "What is most amazing is that most of them did this on the first trial.
"The first time we gave them the problem, six out of seven tried to do the right thing.
"They took the little tool and they tried to get the big tool out, which we had made quite hard to reach, and four out of the six managed to get the big tool out and then use this to get to the food."
In another experiment, the positions of the long and short twigs were reversed.
The team found that all apart from one crow briefly attempted to use the long twig to try to retrieve the short twig from box before quickly correcting their mistake and using the long twig to directly access the food.
The scientists said the crows' performance was comparable to that of the great apes in similar experiments.
The team believes that because the birds were able to solve the problem on their first attempt they were using analogical reasoning rather than trial and error.
Analogical reasoning is the process of solving a problem using experience gained from solving related previous problems.
Professor Gray said: "The birds were making an analogy: instead of using a tool to get food they used the tool to get another tool to get the food."
This kind of reasoning, added Professor Gray, was commonly seen in humans and possibly in great apes.
"It might explain why the New Caledonian crows - out of all the crow species in the world - only these crows routinely make and use tools," he said.
"It is just a puzzle why this one species on this island in the middle of the South Pacific can do this amazing thing - and we don't really know the answer to this."