Researchers have shown that crows from the South Pacific can learn to use three tools in succession to reach some food, demonstrating an advanced way of thinking.
Scientists at the University of Auckland in New Zealand said the New Caledonian crows, which use tools in the wild, have shown that they are able to develop new behaviours to solve problems.
"It appears that the crows have some kind of complex cognitive mechanism that allows them to generate innovation," said Alex Taylor, lead author of the research, published this week in the Proceedings of the Royal Society B.
The crows from the South Pacific island of New Caledonia are the only birds known to make and use tools in the wild. They carve branches into hooks and tear apart leaves to make tools to get hard-to-reach food.
Taylor said apes, parrots and crows all display a greater ability to generate new behaviours than related species.
Researchers have wondered whether these animals are faster at learning through trial-and-error or if their brains are wired for problem solving.
Taylor said previous research has given weight to the theory that they're wired to learn new behaviours, but the subject is controversial.
In their experiment, the temporarily captured seven wild New Caledonian crows and presented them with a complicated problem that could only be solved by using a number of tools in a specific order.
The birds were placed on a perch, and tied to the perch was a string. A short stick was tied to the end of the string.
A long stick was placed out of reach, behind bars, but close enough that it could be reached with the short stick. Finally, a scrap of meat was placed out of reach of the bird, far enough that it could not be reached with the short stick, but could be reached with the long one.
The seven birds were split into two groups. One group was given a chance to try out each of the individual steps in the problem before being presented with the complete task.
All three birds in the first group were able to reach the meat using all three tools on the first attempt.
The second group was given problems where a piece of meat was attached to a string, and where a stick could be used to reach a piece of meat.
"These crows had never pulled up a tool on a string before and they had never used one tool to get another tool," said Taylor.
All these birds were able to reach the meat at the end of the multi-step task, as well, two of them on them first attempts.
One bird, named Sam, spent nearly two minutes inspecting all of the tools and bars before completing the three steps without any mistakes. Another bird, Casper, was confused by the string at first, but was able to complete the task on the first try.
The other two birds solved the problem on their third and fourth attempts.
Taylor said the birds used their previous experience pulling on string to get food and using sticks to get food to come up with new behaviours.
"They showed the ability to use behaviours in a new context," said Taylor.
Taylor said that an animal using and even making a single tool could be explained by simple learning processes, but the crows solving a set of linked problems, one after the other, using three different tools, show more complex intelligence.
"They were understanding about how tools can be used in a more abstract sense," said Taylor.
Tool use is usually associated with primates and birds, but other species may be able to use objects for specific tasks.
In 2009, Australian scientists discovered an octopus in Indonesia that collects coconut shells for shelter, even carrying them from one place to another, although there was some debate about whether this constituted tool use.