Emus have an image problem, thanks to Rod Hull’s aggressive puppet and the frequently repeated claim that they are the world’s stupidest bird.

But the large flightless birds have shown they are pretty intelligent and can figure out a puzzle, when the prize is a delicious lettuce.

Researchers gave three emus, four ostriches and two of their close relatives, called rheas, a test using a wheel which could be spun to uncover a chamber with a lettuce leaf inside.

All three emus figured it out in their first attempt, biting or pecking the wheel to move it.

Scientists say it shows they are not so bird-brained after all.

British people of a certain age may find it hard to forget entertainer Rod Hull’s mute Emu puppet violently attacking chatshow host Michael Parkinson.

But it was a rhea which used the most aggressive tactic to try and nab some lettuce.

The bird, aptly named Rascal by researchers, twice grabbed the bolt at the centre of the wheel blocking the food, and vigorously shook it, causing the wheel to fall off within five seconds.

But the rhea abandoned this technique after figuring out how to turn the wheel.

The ostriches in the study did not solve the puzzle, which researchers suggest may be because they are less interested in lettuce than emus or, as taller birds, would have had to bend uncomfortably to turn the wheel.

However it may be that they weren’t clever enough, as they have small brains which are only about the size of a walnut.

Crows and parrots have very large brains compared to their small bodies, which is why they are so clever and can teach themselves to use tools.

Dr Fay Clark, who led the study from Bristol University, said it is the first time that emus, ostriches and rheas, which are from a group of birds called ‘palaeognathae’, have been found to complete tricky problems.

She said: ‘This is low-level or simplistic intelligence, from trial and error attempts at a task, and not as complex as the innovation we see in crows and parrots, but it’s a very important finding.

‘These birds had been seen as stupid, when that is not the case.’

The study, published in the journal Scientific Reports, involved birds Noah’s Ark Zoo Farm in Somerset.

Among these, three emus and one rhea moved the wheel in the right direction to get food 90 per cent of the time that they twisted it.

The rhea which violently pulled apart the wheel instead was judged to have found an additional ‘innovative technique’ in a lucky accident.

This behaviour is not seen among rheas in the wild.

Because the birds in the study have been on Earth longer than birds in the biological group containing crows and parrots, their abilities may provide an insight into the intelligence of the dinosaurs, which they are more closely related to.

The emus, ostriches and rheas have such small brains for their size because their parents do not stay with them for long, and so they learn less as young birds, and need less brainpower.

But, in 391 attempts, the emus, which researchers called Donna, Tanya and Rosie, solved the wheel puzzle 11.5 per cent of the time.

The rhea, Rascal, when twisting the wheel instead of wrenching it off, solved it 19 per cent of the time.

The study comes after academics at the University of Exeter said conceptions about donkeys like Shrek’s sidekick are ‘deeply unfair’, as they are often portrayed as stubborn and stupid.