KEY POINTS:
Scientists have revealed an unexpected candidate for the title of the world's second smartest creature - the raven.
According to two researchers, a bird brain is no longer a sign of stupidity; indeed, it could be a sign of surprising intelligence.
In the latest issue of Scientific American,
Dr Bernd Heinrich and Dr Thomas Bugnyar - scientists based at Vermont University in the United States and St Andrews University in Scotland, respectively - reveal a series of experiments that provides startling backing for the idea that ravens are the brainboxes of the natural world.
"These birds use logic to solve problems, and some of their abilities even surpass those of the great apes," they say.
One experiment involved ravens which were allowed to sit on perches from which pieces of meat dangled from string. To get a treat, a raven had to perform a complex series of actions: pull up some of the string, place a loop on the perch and hold it with a claw, then pull up another section of string and hold that loop on the perch.
By repeating this process half a dozen times, a raven could reach the end of the string and getthe meat.
"Some animals can be taught how to get food this way," Dr Heinrich said.
"However, I found ravens could perform this complex sequence of actions straight away. I was extremely surprised the first time I saw one of them do this.
"These birds have never seen string before or encountered meat hanging this way, yet they worked out exactly what they needed to do to get a treat."
Many animals, birds and insects were capable of carrying out complex actions: nest-building, for example. However, such creatures are programmed genetically to undertake the different steps involved in such behaviour. Little intelligence is involved.
By contrast, ravens had demonstrated they could work out complex sets of actions, involving no tests or trial and error.
This implied that they can use logic.
Other experiments by biologists have shown that ravens often let other animals do work for them.
In the wild, they have been known to make calls that bring wolves and foxes to dead animals so that these large carnivores can break the carcass apart, making meat accessible to the birds.
Scientists such as Dr Heinrich and Dr Bugnyar believe that ravens evolved their high intelligence because of their complex social lives and scavenging lifestyles.
The birds have to be able to assess very quickly how close to a wolf or fox they can get when one is eating a dead animal: they need to get close enough to get food, but not be attacked themselves.
However, Dr Heinrich cautioned against stating unequivocally that the raven is the cleverest animal on Earth after humans.
"It is up there with the great apes and dolphins," he said, "but I think it is very difficult to say which is cleverer.
"There are different types of intelligence."
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