A first look at sound transmission through the elephant middle ear—Not what we expected

Abstract

Elephants, the largest terrestrial mammals, have the lowest frequency auditory system, even lower than previously thought, which likely facilitates their long-distance communication. We used a 3D laser Doppler vibrometer to quantify ossicular motions of cadaveric middle ears of both African (Loxodonta africana) and Asian (Elephas maximus) elephants as well as humans to understand the mechanics of sound transmission in animals with larger ears than humans. Velocity in the x, y, and z directions from the umbo and stapes over the 7–13,000 Hz range were converted to their anatomical piston directions. The magnitude of umbo velocity was an order of magnitude greater in elephants than humans below the elephant middle ear resonance of about 300 Hz, whereas the stapes velocity was 5 times greater. These higher magnitude velocities are most likely due to an eardrum that is 7 times larger. Despite elephant ossicles being 10 times heavier, the magnitude of stapes velocity above 1 kHz in elephants and humans was similar, but even more surprising, elephants showed much more group delay than anticipated. We present our results in the context of eardrum size, ossicle mass, the malleus-incus lever ratio that characterize elephant and human middle ear sound transmission. [Work supported by the Amelia Peabody Fund and K01 DC017812.]