Tourists delight in the strange chirping echoes they produce when they clap their hands at the base of the steep staircases that sweep up the face of Kukulkan, a 1,300-year-old Mayan pyramid in the Yucatan. While amusing themselves, the tourists may unwittingly be replicating an ancient Mayan ritual, says David Lubman, an acoustical consultant based in California. The echoes are eerily reminiscent of the call of the quetzal, a bird the Maya considered a representative of the gods. Lubman recorded the enigmatic echoes while on vacation in Mexico and analyzed them when he returned home. The echoes sound like chirps, he realized, because the sound from the clapping doesn't hit a solid wall but hundreds of small steps, producing hundreds of echoes. The difference in the distance traveled by echoes bouncing off lower steps is rather small, so the echoes follow each other closely and make a high-pitched sound; the distances and intervals between successive echoes returning from the higher steps, however, are longer, so their pitch is lower. When the echoes reach a listener's ear, the change in pitch sounds like a chirping bird.
The dimensions of the steps, it turns out, are the key to the effect. Each step is tall, but the tread, where the foot is placed, doesn't cut deeply into the pyramid. If the stairs were deeper and not so high, the effect on the echoes would not be as great, and they wouldn't sound like a chirp. That Lubman noticed the similarity between the echo and the quetzal's call was a "lucky hunch," he says, but the Maya, he thinks, knew exactly what they were doing when they built the staircase at Kukulkan. "For about 1,000 years before this, they had been building stone staircases in the open, where you are going to get an echo," he says. "All it would take is one person in 1,000 years to notice that when you shorten the staircase tread, the pitch of the tone rises." The Maya could have used the sound in ceremonies conducted at the pyramid, which was clearly linked to the sacred bird. Kukulkan is a Mayan deity whose name shares the same root as the Mayan word for "quetzal" and who is often depicted with the bird on his back.
Archeologists had always considered hand-clapping tourists a nuisance at Kukulkan, but now some are admitting that Lubman's theories are possible. "The Maya were people of the forest, where it was really important to listen," Lubman says. "The visual sense has been dominant in our culture, but there's much to be gained if historians learn that ears were more than mere pegs for jewelry."