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Jessica L. Barker, Digest: Songs of the sea: Mammalian vocalizations in aquatic and terrestrial environments, Evolution, Volume 71, Issue 2, 1 February 2017, Pages 489–490, https://doi.org/10.1111/evo.13161
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Animals from a wide range of vertebrate taxa communicate using vocal signals. Vocalizations themselves are also highly diverse, from the repetitive calls of a chorus of frogs to a sequence of mimicry by parrots. Why are different species’ vocalizations so different from each other?
First, the form of any signal is affected by selection for clear transmission from sender to receiver, that is signal efficacy (Maynard Smith and Harper 1995). For all acoustic signals, this involves sound waves propagating through the environment via vibrating molecules; this occurs more easily through liquids than through gases. Second, signal form is affected by mechanisms of production and reception. That is, physiological characteristics of both senders and receivers may act as constraints: for example, the frogs’ chorus is constrained by production from a throat sac (Bradbury and Vehrencamp 1998).
The form of acoustic signals varies along many axes; one major axis of variation is frequency. While humans’ hearing range is from 20 Hz to 20 kHz, many animals’ vocalizations exceed this range, from elephants’ infrasound rumbles to bats’ ultrasonic echolocation. Animals are generally constrained to produce vocalizations with wavelengths not longer than their body size, meaning that frequency scales inversely with body size (Bradbury and Vehrencamp 1998). In addition, a sound's optimal frequency depends on the environment in and distance over which it is transmitted.
