Chameleons change colours in unusual ways when they interact with each other to convey different types of information during important social interactions, according to a first of its kind study.
Arizona State University researchers found when male chameleons challenge each other for territory or a female, their colouring becomes brighter and much more intense.
Males that display brighter stripes when they are aggressive are more likely to approach their opponent, and those that achieve brighter head colours are more likely to win fights.
Also, how quickly their heads change colour is an important predictor of which chameleon will win a skirmish, they found.
Russell Ligon, a doctoral candidate in ASU's School of Life Sciences, and Kevin McGraw, an associate professor in the school, used photographic and mathematical modelling tools in new ways to study how the colour change of veiled chameleons (Chameleon calyptratus) relates to aggressive behaviour.
They studied the distance, maximum brightness and speed of colour change of 28 different patches across the chameleons' bodies.
"We found that the stripes, which are most apparent when chameleons display their bodies laterally to their opponents, predict the likelihood that a chameleon will follow up with an actual approach," said Ligon.
"In addition, head colouration - specifically brightness and speed of colour change - predicted which was lizard was going to win," Ligon said.
Chameleons typically have resting colours that range from brown to green, with hints of yellow, but each chameleon has unique markings. During a contest, the lizards show bright yellows, oranges, greens and turquoises.
Interestingly, when the chameleons showed-off their stripes from a distance and followed that display with a "head-on" approach before combat, the important colour signals on the striped parts of the body and head were accentuated.
"By using bright colour signals and drastically changing their physical appearance, the chameleons' bodies become almost like a billboard - the winner of a fight is often decided before they actually make physical contact," Ligon said.
"The winner is the one that causes its opponent to retreat. While sometimes they do engage in physical combat, these contests are very short - five to 15 seconds.
"More often than not, their colour displays end the contest before they even get started," Ligon said.
There are approximately 160 species of chameleons in the world. Veiled chameleons (Chameleon calyptratus) are native to the Arabian Peninsula - specifically Yemen and Saudi Arabia.
They are omnivorous and live essentially solitary lives except when mating.
The results of the study are published in the journal Biology Letters.
