Page last updated at 08:37 GMT, Tuesday, 25 November 2008

Press-ups key to lizard language

By Rebecca Morelle
Science reporter, BBC News

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The latex lizard was programmed to first do press ups and then typical territorial displays while other lizards looked on

A robotic lizard has helped to unravel the secrets of how their real-life counterparts "talk" to one another.

Using the latex creation, US scientists found that anole lizards perform eye-catching press-ups as part of their communication strategy.

The team says the reptiles use this display when faced with poor visibility to catch their neighbour's attention before relaying more detailed messages.

The research is published in the journal PNAS.

Male yellow-chinned anoles (Anolis gundlachi), which are found in the forests of Puerto Rico, advertise their claim of a choice piece of tree-trunk by bobbing their heads and puffing up their brightly coloured dewlaps (the flap of skin that sits under their throats).

There isn't much point in producing these broadcast displays if nobody can see them
Terry Ord

But this territory-marking sign language can often be obscured by dense vegetation and poor lighting.

Terry Ord, from Harvard University and the University of California, Davis, who is the lead author of the paper, said: "There isn't much point in producing these broadcast displays if nobody can see them."

The problem is even more acute for visual communication than for acoustic communication.

Dr Ord explained: "With acoustic communication, you can call and you don't necessarily have to be facing the signaller.

"But in the visual domain, these guys have to attract the attention of who they are trying to communicate with, so that they can then orient towards the displayer and perceive the rest of the display."

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Here, a real lizard does some eye catching press ups

While in Puerto Rico, the team had already observed that anoles sometimes performed a series of press-ups before commencing their typical territorial displays.

"We wanted to see if they were using these press-ups to attract attention to the message part of their display," explained Dr Ord.

To do this, the researchers turned to a hand-painted, latex, mechanical robo-lizard for help.

This construction not only looked just like a real anole, but was able to precisely imitate its displays.

This is the first time the phenomenon has been shown in lizards
Terry Ord

The scientists positioned the robotic reptile on a prime bit of tree trunk, and programmed it to display both with and without introductory press-ups before conveying its territorial message.

In high visibility, the addition of press-ups made little difference to how quickly nearby flesh-and blood anoles spotted the displaying robot.

However, when visibility was difficult, the eye-catching preview made a "dramatic difference".

Dr Ord said: "In these conditions, the lizards would orientate towards the robot within the first one or two movements of the alert display.

"They would turn around, spot the displaying robot, and then pay attention to the message component of the display.

"When the alert wasn't added, sometimes they would spot the robot quickly, but usually they would only turn around in the middle of the message or even miss the message completely."

In low visibility, using an "alert" to precede a message seemed to be essential to getting the key information across, the team concluded.

Dr Ord said: "We have known about this idea of alerts for a long time, but this is the first time the phenomenon has been shown in lizards.

"What's really interesting is the anoles are in some way assessing the environmental variables that are likely to affect the detection of their signals and they are tailoring their behaviour accordingly."

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