David G. Browning - decibeldb@aol.com
Department of Physics
University of Rhode Island
Kingston, RI 02881
Peter M. Scheifele - scheifel@uconn.edu
Department of Animal Science
University of Connecticut
Storrs, CT 06269
Popular version of paper 2pAB4
Presented Tuesday afternoon, May 25, 2004
75th Anniversary (147th) ASA Meeting, New York, NY
Generally their cousins (horses, zebras) are relatively quiet, relying on keen eyesight and speed for safety. Even female donkeys (jennets) are subdued but no one can miss the loud "hee-haw" of a male (jack) donkey!
This characteristic sound (bray) is produced by vocalizing both on the exhaling of air (producing the "haw") and also - and this is what makes it unique - on the inhaling of air too (giving the "hee").
In contrast to the relatively uniform sounds of other farm animals, such as the bleating of sheep or the mooing of cows, the brays of donkeys were found to be highly variable, ranging from the familiar balanced hee-haw, to extended haws with very brief hees (as in the latest Superbowl commercial), or very strong hees followed by relatively quiet haws. This is somewhat surprising as they appear to be produced reflexively (as are cow moos) just by "letting her rip".
Frequency analysis reveals that donkeys can either start their brays with a strong inhaling of air followed by a more relaxed exhale (hee-haw), or a strong exhale (essentially a bellow) followed by a relaxed inhale (haw-hee). Either strong effort results in an arching of frequency with time, in other words the frequency increases until the maximum air outflow/inflow is reached and then falls back (similar to what is seen for a cow's bellow). For the relaxed part the shape is just the opposite (concave), lowering then coming back.
At times donkeys give an apparently uncontrolled series of brays which ends when the animal is out of breath, essentially having a "fit", whether this is caused by frustration as in the human case, has yet to be determined.
As with many animals, we are just starting to appreciate the uniqueness of donkey vocalizations, as well as the similarities with close species (for example the frequency spectra of a "haw" is similar to a horse's "whinny") and perhaps surprisingly some distant ones - the other creatures that share the ability to bray are African and Humboldt Penguins !!