Famous Sad Love Quotes: Do not disturb: Monkeys invent new method of communication by covering their eyes when they want to be left alone

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A 15-year-old female mandrill invented the unique gesture at Colchester Zoo in Essex
It was then picked up by other members of the group

By Andrew Levy

Last updated at 2:24 PM on 4th August 2011

When a monkey started covering her face with her hands, some zoo staff thought she was plagued with poor eyesight.

Another theory was that the mandrill was shading her eyes from the sun.

But now an American expert has suggested the 15-year-old female, called Mandy, invented a unique gesture to tell other monkeys at Colchester Zoo in Essex that she wants to be left alone.

Remarkably, the signal has been picked by other members of the group when they too require solitude.

Covering her eyes: A 15-year-old female mandrill, called Mandy, invented the gesture to tell other in Essex that she wants to be left alone

Mark E Laidre, an evolutionary biologist at the University of California, believes it is evidence of social culture among the mandrills, which are the largest species of monkey and are best known for the eye-catching colouring on their faces and behinds.

It has not been spotted among other primates and is unlikely to have been influenced by human activity as, unlike apes, dolphins and dogs, mandrills do not mimic human behaviour.

Mr Laidre expects other researchers will now find other monkeys using cultural gestures - suggesting 'the capacity to communicate with the hands in a meaningful way may have existed a long time before humans came on the scene'.

Zookeepers first notice Milly, a shy, low-ranking member of her group, covering her eyes - mimicking the famous 'see no evil' gesture - in 1999 when she was three.

But it was only when Mr Laidre spent 100 hours studying the mandrills during 2007 and 2008 that he noticed the significance.

'I saw this behaviour in the first few hours. I'd never seen this before - I knew it was very interesting,' he said.

'By covering their eyes with their hands, individuals possibly conveyed to others that they wanted to be left alone and this message may have been respected as a "do not disturb" sign.'

Unique: The gesture has not been spotted among other primates and is unlikely to have been influenced by human activity

The gesture involves placing the hands loosely over the eyes but with the fingers parted to be able to keep watch on their surroundings.

They last between six seconds and 30 minutes, during which the rate at which others approach or touch the individual drops dramatically.

They can happen anywhere in the five living areas the monkeys have - only one of which is on show to the public – and equally when the animals are sitting alone or with others.

Monkeys that rank lower in the social order also appear to use the technique to avoid attacks from more dominant individuals.

Culture accounts for behavioural differences that are geographic, rather than genetic or environmental. Gestures - non-vocal, communicative actions - are often cultural in humans and sometimes in apes.

The unique discovery at Colchester Zoo, where there are 25 mandrills, suggests it is a local phenomenon that arose naturally and is used to convey information within the mandrill community.

Curator Sarah Forsyth said: 'We believe Milly made up the signal and over the past five years some of the younger mandrills have picked it up.

'We're not sure why she started doing it but it could be as simple as "I can't see them, so they can't see me".'

She added: 'It really does show you how intelligent mandrills are.

'We were teaching the dominant male, Dume, to open his mouth and he picked it up in only a few days. Now he comes up to us with his mouth open wide because he knows he will get a treat.

'The hand over the eyes gesture is the only one invented by the group but it hasn't been seen anywhere else. They really are extraordinary monkeys.'

Mandrills are found in the rain forests of southern Cameroon, Gabon, Equatorial Guinea and Congo, where they live in large groups often hundreds strong.

They live around 20 years in the wild and adults typically grow to about 3ft tall and weigh 77lbs.

Experts have been forced to reassess their assumptions about animal intelligence following a series of fascinating discoveries.

These include animals using tools such as otters, which smash molluscs on rocks to get at the meat inside, and crows which have bent wires to fish a basket of food from the bottom of a plastic tube.

In 2009, a zoologist at Cambridge University found a rook could work out that dropping stones into a container filled with water raised the level enough to be able to drink from it.