Category: Vocalization & Song

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Vocalization (a form of animal communication that involves the vocal cords or equivalent such as the bird syrinx) and song (characterised by a regular pattern of motifs and syllables) play an important role in the lives of many animals. Best known probably from birds, frogs and cetaceans (whales and dolphins), these vocal utterances can fulfil various functions in communication. Male animals often defend territories and attract mates by singing or calling, while in many species individuals use alarm calls to alert others to the presence of a predator. Vocal signalling is also important in parent-offspring interactions, particularly in birds and mammals. It has been hypothesised that vocal communication could have evolved independently in these two groups in relation to parental care.

Generally, vocalization and song often show convergent evolution. One of the most obvious examples is the similarity between human music and the songs of humpback whales and birds. Humpback whale songs seem to be constructed according to laws similar to that employed by human composers, while both human and bird songs show features such as simple harmonic relations, interval inversions and retention of melody with change of key. Canons are reminiscent of bird countersinging, and there are even regional dialects in birds. Interestingly, song has not only evolved once within the birds but at least three times, as indicated by the independent evolution of similar forebrain structures involved in song production in songbirds, parrots and hummingbirds.

Similar neural mechanisms are likely to be involved in bird song and human speech. According to a study by Doupe and Kuhl (1999, Annual Review of Neuroscience, vol. 22, pp. 567-631), there are anatomical and functional parallels in the organisation of neural pathways, similar interactions between sensory and motor processes, and learning is enhanced during a critical period early in life. This is particularly remarkable as avian and mammalian brains differ clearly in structure.

With respect to vocal learning, there are strong parallels between dolphins and humans, including a babbling phase (and this is also seen in some birds). While cetacean vocalisations are generally complex and varied, there is evidence that dolphins are competent in both semantic and syntactical modes. Given instructions of a string of "words" (which may be transmitted by hand signals or underwater sounds) the dolphin will perform the appropriate action. Even when the same "words" are re-ordered to give a new "sentence" structure, the correct command is obeyed. Many dolphins produce whistles, the function of which is not fully understood. Dolphins in the genus Cephalorhynchus, however, do not whistle but have vocalisations convergent to those of phocoenid porpoises.

Dolphins communicate in the ultrasound range, but the ability to communicate ultrasonically is rampantly convergent. Most familiar are the various mammalian groups, not only cetaceans but also (and most famously) bats and even rodents. Amphibians are adept at vocalization as well, and remarkably ultrasonic communication has evolved in a species of frog, the concave-eared torrent frog from China. As its name suggests it inhabits fast-flowing streams and it is assumed that the "diverse bird-like melodic calls" (Feng and Narins, 2008, Journal of Comparative Physiology, vol. 194, pp. 159-167) that extend into the ultrasound enable the frogs to be heard above the sound of rushing water.

Song production does not necessarily require vocal cords. Several groups of animals produce sound by stridulation, the rubbing together of certain more or less specialised body parts. This is best known from a number of insects (most famously grasshoppers) but can also be found in some snakes, tarantulas and even one species of bird, the club-winged manakin. Acridid grasshoppers normally sing by rubbing their hind-legs against the forewings or the abdomen, but one species produces the same song by rubbing the mandibles. On a more distant note, parasitoid flies using a specific cricket host have convergently evolved a hearing organ much more similar to a cricket ear than to a typical fly ear in order to find a singing male cricket on which to deposit their maggots.

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Topic Title Teaser text Availablity
Echolocation in bats

How can bats navigate in total darkness amongst trees and branches, but still locate a tiny, fluttering insect with extraordinary acuity? All made possible through echolocation, an astonishing sensory mechanism…

Stridulation in insects and other animals n/a Not Available
Echolocation in birds: oilbirds and swiftlets

The best known example of echolocating birds are the South American oilbirds (Steatornis caripensis), so called because their flesh yields abundant oil.

Bats: Insights into convergence

Bats show a fascinating array of convergences, from echolocation to flight to nectar feeding. Vampire bats can even detect infrared radiation, while others might be able to see into the ultraviolet end of the spectrum.

Echolocation in toothed whales and ground-dwelling mammals

Given the extraordinary powers of echolocation in bats, it is not surprising that this group has received the most attention. However, they are not the only mammals to have evolved echolocation. Who invented sonar millions of years before the Navy?

Bird song n/a Not Available
Dolphin communication, cognition and sociality

Dolphins are one of the most intriguing sources of evolutionary convergence, having cognitive abilities that seem to find many parallels in the great apes, and rather remarkably even extend to tool use.

Elephants: senses, intelligence and social structure

There is evidence that elephants are sensitive to seismic communication, with the large pads of the feet and the trunk tip capable of picking up vibrations transmitted through the ground.

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Ultrasound communication in mammals and amphibians

Amphibians are adept at vocalization, and remarkably ultrasonic communication has also evolved in the Concave-eared torrent frog, from China.

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