"Basically there's a neurological control mechanism that stimulates the pigments" to move around and cause the chameleon's skin color to change, Anderson explained.
Whether chameleons are actively aware of their color changes is an open question, Anderson said. He suspects that the ability to do so is a trait borne out through the process of natural selection.
Camouflage and Communication
Raxworthy, the American Museum of Natural History herpetologist, says understanding why and when chameleons change color is an ongoing scientific pursuit that began with field observations in the 1960s.
He says the lizards' rapid changes in color, which can occur in about 20 seconds, are most dramatic when chameleons are interacting with one another. He adds, though, the changes also play an important role in allowing the lizards to hide or blend in with their environment.
"Most of the time, chameleons are behaving as highly cryptic animals trying to avoid detection from predators," he said.
In a broadcast of the Pulse of the Planet radio program airing today, Raxworthy says the best time to find chameleons is at night, because they turn pale then and are easily illuminated with a flashlight.
(The National Science Foundation funds the radio program and this related National Geographic News series.)
When asked precisely why the lizards turn pale at night, Raxworthy says, "We are not sure. But it seems to be related to the closing of the [chameleon's] eyes."
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