What bearded dragons tell us about color and heat

A Central bearded dragon (Photo: Devi Stuart-Fox)

A Central bearded dragon (Photo: Devi Stuart-Fox)

Dr. Devi Stuart-Fox has spent more than 15 years investigating how and why lizards change color. She’s studied how gliding lizards use the sun to show off their colors, whether bearded dragons change color in their sleep (they do), and how female bearded dragons avoid mating (display a bright orange pattern on their bellies).

“Those of us who study animal color, don’t just look at colors in isolation — we look at colors relative to each, relative to the background and relative to the illumination,” she says in a talk at TEDxStKilda.

Below, some insights into bearded dragon color change from Stuart-Fox’s talk:

Bearded dragons “dress” for the weather by changing colors.

Bearded dragon in different temperatures (Photo: Devi Stuart-Fox)

A bearded dragon in different temperatures (Photo: Devi Stuart-Fox)

Stuart-Fox and colleagues used an incubator to see how bearded lizards react temperature — and found that the lizards make themselves dark in the cold and light in the heat.

Because darker colors absorb more energy, lizards turn pale to avoid overheating, like avoiding wearing a black t-shirt on a hot summer’s day. They turn dark in the cold “to heat up faster and become active,” Stuart-Fox says.

Bearded dragons communicate via color — in strategic ways.

When threatening other lizards, a bearded dragon turns his throat black (Photo: Devi Stuart-Fox)

When threatening other lizards, a bearded dragon turns his throat black (Photo: Devi Stuart-Fox)

Through their experiments, Stuart-Fox and her team found that bearded dragons only change their belly color in response to heat. When socializing, the lizards isolate their color changes to a strategic area — their neck — turning their “beard” black as a way to communicate and fight with other lizards.

Bearded dragons can change how their skin reflects near-infrared light, even though they can’t see it themselves.

Colors may look the same, but have different effects (Photo: Devi Stuart-Fox)

Colors may look the same, but on the near-infrared scale, be quite different  (Photo: Devi Stuart-Fox)

We can’t see near-infrared light and neither can bearded dragons. In fact, no animal can, says Stuart-Fox. Nevertheless, bearded dragons can change the way their skin reflects this spectrum of light, to more acutely balance their temperature.

Two things that are black in the visible spectrum of light can be completely different in the near-infrared, Stuart-Fox says. And two colors that look completely different in the visible spectrum can be exactly the same in the near-infrared. Which is why it’s so incredible that these creatures can tweak their near-infrared colors: “Not only can they hone their visible color for communication or camouflage,” she says, “but they can change how their skin reflects visible and near-infrared light.”

 To learn more, watch Stuart-Fox’s whole talk below:

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