Resplendent Quetzal

Long before the MP3 format, even before Compact Disks, the Mayans of Chichen Itza in Mexico built the Temple of Kukulkan, a pyramid with a series of oddly high, narrow steps. Acoustician David Lubman discovered that if you stand in front of the staircase and clap your hands, the impulse response sounds reminiscent of the mellifluous descending chirp of the Resplendent Quetzal, the Mayan sacred bird.

Listen to a recording of two Quetzal calls, followed by two handclap echoes (with the actual handclaps removed).

The Quetzal is considered to be the most beautiful bird in the western hemisphere. When flying across an open patch of sky, it shimmers in the sunlight with patches of red, gold, silver, and utterly impractical iridescent green streamers three feet long. The emerald green is actually brown, but the feathers have ripples that are spaced at the wavelength we see as green. Iridescent feathers, like those of Quetzals and hummingbirds, have slightly different colors depending on the angle from which they’re viewed, because the viewing angle changes the relative distance between the ridges.

A similar phenomenon in the acoustic domain is responsible for the chirped echoes from the Kukulkan staircase: periodic reflections from the stepfaces produce what is known as a Bragg diffraction grating (or, more popularly, the “picket-fence effect”), with the pitch of the tone determined by the spacing of the stairs. The wavelength reinforced by the low stairs directly in front of you equals the horizontal distance from one step to the next, but higher up on the stairs the angle changes, increasing the wavelength and lowering the pitch. The downward chirp occurs because the low echo frequencies (which reflect from further up the stairs) are delayed more than the high frequencies. The beginning and ending pitches happen to be a close match to those of the Quetzal's call.

The steps of the Kukulkan temple appear to be made of an oddly resonant stone, and the Chichen Itza pyramids are known for other interesting acoustic effects, including voice transmission over long distances. Certainly the Mayans would not be alone in the use of architectural acoustics to reinforce the authority of their kings and religious leaders.

Did the Mayans intentionally engineer this pyramid to capture the voice of the Quetzal, thus creating the world’s oldest sound recording? Lubman learned that some modern Maya are familiar with this echo and refer to it as "la cola del Quetzal," the Quetzal’s tail. It is not inconceivable that the ancient Maya may have experienced this picket-fence effect from another staircase and refined the spacing of the stairs to match the pitch of the Quetzal. Nevertheless, lacking written evidence, this may forever remain fascinating speculation.

The Quetzal is the national bird of Guatemala and is considered endangered.


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