Male alligators use a deep, sexy rumble to attract females, a sound so deep it is inaudible to the human ear, a University of Florida researcher says.
The discovery may be a key to showing that many animals, from whales to grouse, use such sounds to communicate over distances once thought impossible, said UF biologist Kent Vliet.
With alligators, females feel as well as hear the vibrations. During courtship, females will rest their chin on the throat or neck of the male and often close their eyes, signs they are enjoying the vibrations that pass through their bodies, Vliet said.
"It's quite a sexual turn-on for females to feel the power of these vibrations, and they will do just about anything they can to stimulate the males into courting and mating with them," he said.
The powerful low-frequency signal accompanies the toothy reptiles' love bellows, which become increasingly frequent as alligator courtship season peaks this month, he said.
Understanding these "infrasounds," frequencies too low for human ears, may revolutionize scientific thought about alligator communication and social order, Vliet said.
"Obviously, we can't understand alligators' social organization and communication thoroughly without an understanding of infrasound," he said.
He and Katie Payne, a Cornell University scientist, detected the signals for the first time by recording about 800 alligator bellows and feeding them into computers programmed to analyze sound frequencies.
"So much energy is produced from this acoustical vibration that water spews up as much as a foot off the surface of the water and dances around the alligator like jets of water from a fountain," Vliet said.
A male alligator produces these low-frequency signals immediately before loud bellows, which often erupt into contagious choruses across Florida lakes in the courtship months of April and May, he said.
A handful of other animals have been shown to use infrasound, including elephants, hippopotamuses and a species of grouse.
In elephants, the phenomenon was discovered in zoos when people standing near the animals would sense vibrations but not hear any sounds, Vliet said.
Recognizing the existence of infrasound in a particular species may force scientists to re-evaluate whether an animal may be communicating over much longer distances than once thought, he said.
Studies on fin whales suggest that infrasonic signals may travel as far as 11,000 miles, making it possible, in theory, for one whale to communicate with any other in an entire ocean, Vliet said.
"Just as pods of whales may be communicating with other pods, alligators in a lake may be communicating with each other over long distances without any signals being exchanged _ at least that are obvious to humans," he said.