Lizards Do "Push Ups" to Get Their Neighbors' Attention

John Roach
for National Geographic News
November 24, 2008
Lizards use "push ups" to attract attention in noisy environments, according to new research that used robotic lizards.

The robots, fashioned to mimic the appearance and body language of live anole lizards, helped scientists confirm a longheld theory that animals use grand gestures, such as the lizard push-up, and loud noises to get the attention of other members of their species in chaotic, noisy environments.

These so-called alert signals are used to cut through environmental noise, according to new research on anoles in Puerto Rico.

These reptiles create exaggerated, eye-catching push-ups to grab their neighbors' attention before using more nuanced head-bobbing gestures to communicate territorial and fitness claims, according to the study.

But the lizards are more likely to do push-ups when visual obstructions or visual "noise," such as low light or blowing branches, would otherwise drown out the head-bobbing.

"They are actually changing their behavior to compensate for those [noises]," said Terry Ord, a research associate in evolution and ecology at the University of California in Davis.

The lizard research clearly demonstrates that animals use visual alert signals, said Ord, who led the study published online Tuesday in the journal Proceedings of the National Academy of Sciences.

Alert signaling is thought to be widespread in the animal world, but had previously only been definitively shown in towhees, a type of bird that sends audible alerts, according to Ord.

Other studies have suggested tree frogs and coyotes also use audible alerts.

(The research was funded in part by a grant from the National Geographic Society's Committee for Research and Exploration. The National Geographic Society owns National Geographic News.)

Lizard Robots

Puerto Rican anole lizards live on tree trunks, often positioning themselves with their heads pointed toward the ground.

Males make a series of head-bobs that let neighboring males know their territorial claim—typically two or three trees that are also home to several females, ensuring the male has mating success.

Since territorial head-bobs are also energy-intensive, previous research has suggested they contain information about the fitness of the displayer, Ord noted.

"If you can produce a lot of these displays then other males are going to know you are in good physical condition" and thus unlikely to mount a challenge, he said.

As Ord was studying this behavior, he noticed that sometimes, but not all the time, the lizards would do the push-ups before starting the head-bobs.

The push-ups, he thought, seemed like an alert display.

To find out, he built realistic, robotic lizards that perform the push-ups, head-bobs, and an unusual display for this species called a dewlap extension.

A dewlap is loose skin that hangs under the lizard's throat.

Ord put these robots in the Puerto Rican forest and observed how the real lizards responded to the various gestures.

Based on an analysis of more than 300 responses, he concluded the lizards use alerts when their neighbors are far away or otherwise visually distracted.

The push-ups and dewlap extensions also elicited a response, confirming the hypothesis that the alerts are just alerts—they don't contain additional information.

In the wild, anole lizards communicate with the push-ups.

"You can imagine doing push-ups takes quite a bit of energy," Ord said. "So they don't always want to [do them] if they don't need to."

In addition, the push-ups might attract predators such as the Puerto Rican lizard-eating cuckoo and feral mongoose.

Theory Confirmation

Leo Fleishman is a biologist at Union College in Schenectady, New York, who uses lizards to study the evolution of communication signals.

He said the study is a "nice confirmation" of earlier studies that indicate lizards initiate communication with highly visible physical displays when the viewer is inattentive and far away.

The new study proves that such motions do elicit the attention of potential viewers, he said.

"And the demonstration that [the lizards] are more likely to add it under a variety of what they call noisy conditions is also novel. The examples before only involved distance," he said.

According to Ord, the lizards may learn the signals via experimentation.

"Over time they'll get an idea that in some conditions they'll get responses from the lizards they're trying to communicate with when they add a particular component to their display," he said.

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