3.04 - Sensory Ecology of Hearing

Abstract

All five classes of vertebrates have hearing mechanisms based on hair cells. These mechanisms vary at several levels. Categorical differences in anatomy and function are found among classes of vertebrates. The same applies within classes, but more variation has been found among fishes, for example, than among birds. Such variation is reflected in hearing performance. In general, mammals tend to have the widest frequency ranges and the lowest thresholds, and fishes have the most limited hearing. However, this generalization is heavily undermined by several factors. Hearing performance varies widely within some classes of vertebrates and species can be found with high performance, low performance, or high performance over a narrow frequency range. Some fishes, for example, can hear ultrasound up to 180 kHz. In spite of the variation in mechanisms, most vertebrate groups have been shown to be capable of resolving direction and elevation of sound sources. Hearing mechanisms and performance evolve in accordance to the medium (air, water, or soil), environmental acoustics, background noise, and the range of detectable sounds that are biologically relevant. Besides adaptations of the hearing mechanism, vertebrates also respond to the variables above with plastic behavior. Hearing performance and associated behaviors are further modulated by endogenous factors such as growth and exogenous factors such as temperature. Background noise, anthropogenic or not, can alter hearing in several ways and produce behavioral and evolutionary adjustment in vertebrates.