Production of Biosonar Signals: Structure and Form

Abstract

The biosonar capabilities of any animal will depend on many characteristics of their biosonar system such as the acuity of the auditory system, the information carrying capacity of the projected signals, the spatial resolution of the biosonar process, the amount of auditory memory, the speed of auditory recall, the degree of coupling between the biomechanics and signal processing systems, and so on. The fi rst of all these factors is the ability to generate or produce signals that will enable the animal to perform the necessary sonar tasks for its survival. This includes the generation of suffi ciently intense signals to receive echoes from prey that are above the background ambient noise environment and the production of signals with the proper information carrying capacity for the specifi c task at hand. Needless to say, the environments that dolphins and whales live in cannot be more different than that of bats, and each environment imposes much different constraints on the biosonar system. At 20 °C the density (ρ) of air at sea level is 1.21 kg m −3 and the speed of sound

Behaviour, biology, and evolution of vocal learning in bats

“…The vocal folds of bats are comparable to other mammals, except that they feature an extended thin membrane that extends the vocal fold upwards. This vocal membrane is also found in some non-human primates [79,80] and is thought to enable high-frequency or ultrasonic call production.…”

“…Because the larynx and vocal tract shape these vocalisations, their morphology and neural control determine the range of possible vocalisations that an animal could produce. The structure of the larynx has been investigated in a number of echolocating bats and is broadly similar to that of other mammals [79,80]. The source-filter model [19] initially proposed for human speech, applies to bats and other mammals; the laryngeal source and the vocal tract filter are considered to be largely independent [79,80].…”

“…There are, however, some notable differences observed in the bat larynx. For example, echolocating bats display superfast laryngeal muscles that facilitate rapid call rates [81] and cartilage in the bat larynx ossifies earlier than in other mammals, which has been suggested to allow them to withstand the mechanical stress of echolocation [79]. The vocal folds of bats are comparable to other mammals, except that they feature an extended thin membrane that extends the vocal fold upwards.…”

Biomechanical control of vocal plasticity in an echolocating bat

“…Physiological foundations of sound production have been intensely studied for a variety of animal species (Suthers, 2010;Bradbury and Vehrencamp, 2011;Au and Suthers, 2014;Elemans, 2014). While the majority of studies focused on the physiological bases of producing distinct vocalization types, the physiological processes responsible for fine adjustments of the same vocalization type are less clear.…”

“…In contrast, our knowledge on how the vocal tract shapes echolocation signals is rather limited and has been investigated only in a few species (for review, see Au and Suthers, 2014). In particularly, it is unclear to what extent the vocal tract is actively used by bats to adjust their calls to variable environments.…”