Lizards that use their bodies' visual displays to signal to rivals are in effect "shouting" to get their point across, UC Davis researchers have found.

The male anole lizard defines his territory by sitting up on tree trunks, bobbing his head up and down and extending his colorful throat pouch. These lizards can spot a rival lizard up to 25 meters away, said Terry Ord, a postdoctoral researcher at UC Davis who works with Judy Stamps, professor of evolution and ecology.

The lizard's signal needs to be strong enough for a rival to see, but not vivid enough to say "eat me" to passing predators. In a visually noisy forest, though, with branches and leaves waving in the breeze and casting patterns of light and shade, the lizard needs "a strategy to get their message across," Ord said.

Ord videotaped two species of anole lizards, Anolis cristatellus and Anolis gundlachi, in the Caribbean National Forest in Puerto Rico. He found that the more "visual noise" in the background, the faster and more exaggerated the movements of the lizards.

Anole lizards are interesting to evolutionary biologists because different species are found on different islands all over the Caribbean. The lizards are not particularly closely related — they are separated by 30 million years of evolution — but they live in similar environments with the same obstacles to communication. So Ord is using them as a model to investigate the evolution of such signals.

The research appears online in Proceedings of the Royal Society part B. Ord's co-authors included Barbara Clucas, a UC Davis graduate student in animal behavior.