IT’S a tough nut to crack, but step by step clever cockatoos solved a series of mechanical problems to get their reward.

The experiment, conducted by scientists from Oxford and Vienna, has revealed new depths of intelligence in the birds.

A team of scientists from Oxford University and the University of Vienna completed a study in which 10 untrained Goffin’s cockatoos faced a puzzle box showing food – a nut – behind a transparent door secured by a series of five different interlocking devices, each one jamming the next along in the series.

To retrieve the nut, the birds had to first remove a pin, then a screw, then a bolt, then turn a wheel 90 degrees, and then shift a latch sideways.

One bird called Pipin cracked the problem unassisted in less than two hours.

A cockatoo called Muppet is pictured solving the bolt-type lock.

The scientists were interested to discover the birds’ progress towards the solution, and what they knew once they had solved the full task.

Prof Alex Kacelnik of Oxford University’s Department of Zoology, a co-author of the study, said: “We cannot prove that the birds understand the physical structure of the problem as an adult human would.

“But we can infer from their behaviour that they are sensitive to how objects act on each other, and that they can learn to progress towards a distant goal without being rewarded step by step.”

The team found that the birds were determined to overcome one obstacle after another, even though they were only rewarded with the nut once they had solved all five devices.