Many animals produce bleating sounds that consist of small and rapid oscillations in frequency, an effect called vibrato when used in human singing. Benjamin Charlton at University College Dublin and his colleagues tested the effect of these trills on humans’ ability to distinguish between sounds.
Speech and animal vocalizations contain characteristic frequency bands called formants, which humans use to distinguish vowel sounds. The team found that rapid frequency modulation improved participants’ ability to detect small changes in the pitch of formants that made up synthetic noises. The authors suggest that this vibrato makes it easier for listeners to distinguish formants, which may carry important information such as the size and identity of the caller. Family trees for 92 mammalian species suggest that such calls evolved separately multiple times, including in carnivores, primates and rodents.