London, September 17 : Presenting six New Caledonian crows with a series of "trap-tube" tests, a team of scientists has come to the conclusion that the bird can use causal reasoning to solve a problem, and is perhaps cleverer than the chimpanzee.
Research leader Alex Taylor and his colleagues at the University of Auckland, New Zealand, placed a choice morsel of food in a horizontal Perspex tube that featured two round holes in the underside, with Perspex traps below.
One of the holes was sealed for most of the tests, so that the food could be dragged across it with a stick, and out of the tube to be eaten.
The researchers left the other hole open, trapping the food if the crows moved it the wrong way.
They observed that despite modifying the appearance of the equipment, three of the crows could solve the task consistently, suggesting that they were not using arbitrary features like the colour of the rim of a hole to guide their behaviour.
The researchers say that the crows seemed to understand that they would lose the food if they dragged it across a hole.
In another experiment, the crows were presented with a wooden table that was divided into two compartments. A treat was at the end of each compartment.
However, in one of the compartments, the treat was positioned behind a rectangular trap hole.
To get the snack, the crow had to consistently choose to retrieve food from the compartment without the hole.
Interestingly, while great apes in a recent study had failed to transfer success at the trap-tube to success at the trap-table, the three crows in the latest study could do so.
"They seem to have some kind of concept of a hole that isn't tied to purely visual features, and they can use this concept to figure out the novel problem. This is the most conclusive evidence to date for causal reasoning in an animal," New Scientist magazine quoted Taylor as saying.
The team plans to continue with its experiments.
The study has been reported in the Proceedings of the Royal Society.