The donkey's characteristic sound is called braying. It is unique among the equids because it requires an ability that donkeys have but horses and zebras lack: vocalizing while both inhaling and exhaling. The hee occurs during air intake, and the haw comes during air outflow.
Despite this sound being specific to donkeys, there is still some variation. The duration and frequency of a bray, for instance, is unique to each individual animal.
- https://www.treehugger.com/facts-will-change-way-you-think-about-donkeys-4869321
