Why chameleons struggle to turn green and blue

By Elizabeth Hunter

Chameleons can change to yellow, orange, and black quickly - but struggle with green or blue, experts say.

Research found the flap-necked chameleon can match certain colors with greater accuracy and speed than others.

The study also revealed that, contrary to their depictions in popular media, chameleons cannot display patterns on their skin.

Researchers identified that the flap-necked chameleon can match yellow, orange, and black backgrounds with much greater accuracy and speed than those that are green or blue.

The study by ecologists at the University of Exeter carried out one of the first laboratory studies of its kind.

Dr. Jolyon Troscianko of Exeter’s Centre for Ecology and Conservation said: "Popular culture often depicts chameleons as masters of camouflage, changing their color to match their backgrounds.

“We know that they use color changing to communicate with one another, such as during the breeding season, and to regulate their body temperature.

"But there has been surprisingly little investigation into their approach to concealment beyond some studies on predator threat."

Chameleons can alter the color of their skin in one of two ways - either through pigment movement or structural color changes within specialized skin cells.

Among the different species, the flap-necked chameleon is renowned for the speed with which it can do this.

For the experiment, eight chameleons were placed individually in a pen that was lined with paper of different colors, hues or pattern treatments.

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The team then took photographs at timed intervals over two ‘runs’ to measure any change in the animal.

This process was repeated across four colors (yellow, yellow-green, orange and blue-green), three uniform grayscale experiments (black, white, and gray), and six pattern experiments.

“We selected hues that were slightly more colorful than typical natural backgrounds to elicit a stronger response from the chameleons, while still preserving biological plausibility,” said Tom Major, who conducted the research at Exeter but is now part of the Department of Life and Environmental Sciences at Bournemouth University.

“Yellow-green and blue-green colors were selected as those which other chameleons can produce, and orange and yellow could be of ecological relevance to flap-necked chameleons, which experience pronounced dry seasons where leaves and grasses may change to these colors.”

The results revealed that the chameleons responded quickly to blacks, reducing their luminescence to blend into the background much faster than when it was white, all within a matter of minutes.

With the colors, the lizards responded steadily and accurately to yellow, but more slowly and with greater variance to orange.

For yellow-green and blue-green colors, which are closer to the chameleon’s natural appearance, the lizards either didn’t change or did so slowly.

The test also revealed that none of the animals sought to match the pattern, regardless of its color or scale.

All of this analysis took into account what is termed ‘predator vision modelling’ – creating a picture as to whether or not a potential predator, such as the fiscal shrike bird, would be able to distinguish the chameleon against the background.

“This ability to change color is likely to have evolved to enable chameleons to move through diverse habitats, in wet and dry seasons, but remain hidden from their predators,” adds Alexia Hesten, also formerly of Exeter, but now of the School of Biological and Environmental Sciences, at Liverpool John Moores University

“But a picture is emerging – based upon these results and what we know of other species – that tells us that these famed abilities have their limits and that maybe chameleons favor the kinds of locations that they instinctively know they can match.”

The research, funded by the University and a European Research Council Consolidator Grant, was published this week in the latest edition of Biology Letters.