David G. Browning, 139 Old North Road, Kingston, RI 02881 firstname.lastname@example.org
Peter M. Scheifele, Dept. of Communication Science, Univ. of Cincinnati, Cincinnati, OH 45267
A bleat is usually defined as the cry of a sheep or goat but they are just two voices in a large worldwide animal chorus that we are just starting to understand.
A bleat is a simple short burst of sound comprised of harmonic tones. It is easily voiced by young or small animals, who are the majority of the bleaters. From deer to polar bears; muskoxen to sea lions, the young bleats produce a sound of enough character to allow easy detection and possible identification by concerned mothers. As these animals mature usually their voices shift lower, longer, and louder and a vocabulary of other vocalizations are developed.
But for some notable exceptions this is not the case. For example, sheep and goats retain their bleating structure as their principal vocalization through adulthood – hence bleating is usually associated with them. Their bleats have been the most studied and show a characteristic varietal structure and at least a limited ability for maternal recognition of specific individuals.
For another example, at least four small varieties of toad, such as the Australian Bleating Toad and in America, the Eastern Narrow Mouthed Toad are strong bleaters through their entire life. Bleats provide them a signature signal that carries in the night and is easily repeatable and sustainable. But why these four amphibians? Our lack of an answer speaks to our still limited knowledge of the vast field of animal communication.
Perhaps most interestingly, the Giant Panda retains bleating while developing a complex mix of other vocalizations. It is probably the case that in the visually challenging environment of a dense bamboo thicket they must retain all possible vocal tools to communicate. Researchers link their bleating to male size and female age.
In summary, bleating is an important aspect of youth for many animals; for some it is the principal vocalization for life; and, for a few, a retained tool among many.