Grabbing someone's attention from a distance is a challenge, particularly under noisy conditions but, according to a new study, anole lizards have devised a successful "look at me" technique: They perform multiple full body, four-legged push-ups to get their fellow lizards to turn their heads.
The exhausting ritual supports the theory that many animals sometimes precede vocal and visual communications with an otherwise meaningless alert signal. It's been suspected that birds, frogs, dogs, coyotes and numerous other animals, including humans, do this.
"The example I give is tapping on glass to get everybody's attention at a dinner before making an announcement, or perhaps whistling loudly to get the attention of somebody at a distance," lead author Terry Ord told Discovery News.
"Another nice example is the emergency radio broadcasts I used to hear when I lived in the Midwest where we would have tornado warnings all of the time," added Ord, a researcher at Harvard University's Museum of Comparative Zoology. He explained that the emergency broadcasts begin with ultra loud tones or beeps followed by the official announcement.
For the study, he and coauthor Judith Stamps observed and videotaped 38 male yellow-chinned anole lizards in the deep-shade forests of Luquillo Mountains in northeastern Puerto Rico.
Earlier this year, the researchers determined that, at dusk and dawn, males of this species plant themselves on elevated perches within their territory to broadcast visual displays to audiences of neighboring males and females up to 29 feet away.
The main signal consists of rhythmic head bobs and flashy displays of their colorful neck flaps, called dewlaps. The underlying message is sort of like a bodybuilder flexing his muscles in front of another bodybuilder. If one male is clearly stronger and fitter than the other, the scrawnier fellow is unlikely to challenge the first individual in a fight, saving a lot of injuries and deaths. The lizard routine also communicates territory ownership.
The scientists noticed that sometimes — but not always — the males would add the exaggerated full body push-up sequence before their usual routine.
To see if the push-ups conveyed any meaningful information, they designed a remarkably realistic-looking anole lizard robot that was programmed to perform the usual head bob display with either the push-ups or a novel dewlap extension intro. Each introductory move got the attention of other lizards, indicating that the push-ups indeed function as an alert.
"Obviously, if nobody is paying attention, performing a territorial display is pointless!" Ord said.
"The lizards add the alerts specifically in conditions when they need to, that is in low light, in visually noisy conditions when the wind is blowing the trees about, and when the individual they are trying to communicate with is at a distance," he explained.
Ord added, "For example, lizards might add alerts when displaying at times earlier in the day when the sun is lower on the horizon and the habitat is dimmer, or if the sun goes behind a cloud, or whenever the wind happens to pick up."
There are at least three reasons why the males don't always add the push-up sequence. The first is it's tiring for them and burns a lot of energy. The second is that, in addition to attracting the attention of other lizards, it could be seen by predators, such as the Puerto Rican lizard-eating cuckoo or the feral mongoose. Thirdly, like the boy who cried wolf, the alert would lose its punch if overused.
The study, funded by the National Geographic Society and the National Science Foundation, is published in the latest Proceedings of the National Academy of Sciences.
Haven Wiley, professor of biology and ecology at the University of North Carolina, also studies animal communication, particularly in birds and frogs.
Wiley told Discovery News that this new report on lizards "is an exciting confirmation of the use of alerting signals in animal communication and of the importance of signal detection theory for understanding the evolution of communication."
He thought the study was "particularly interesting because it showed that adaptations for communication in noise, alerting signals, are used just when you would expect — in noisy conditions."