The call signs of certain dolphins

This being a story built around the dolphins of Shark Bay, a famous sea life flavoured resort on the western coast of Australia. I started with reference 1, working my way through to reference 6. The Morell story at reference 1 is a bit short on references, but she appears to be drawing on references 2 and 3, the first of which I have barely glanced at.

It seems that bottlenose dolphins, certainly the ones in Shark Bay, emit acoustic call signs, whistles of the order of a second in duration, from which they can be identified, presumably by their conspecifics. An underwater version of what, for example, chimpanzees and dogs do by looking and smelling.

The male dolphins use these and other cues to maintain two tier social structures, with a group of the outer tier containing as many as 15 individuals and with these groups sometimes surviving for years. Groups which work together to catch and keep oestrus females. I didn’t get to find out how they shared out the catch.

Dolphin whistles, albeit not from the same species, Tursiops truncatus rather than Tursiops aduncus, are analysed at reference 4, from which the snap above is taken, complete with ‘msec’ for ‘sec’ in the left hand panel. It seems that the relevant information is captured by a plot of fundamental frequency against time and that successful matching of whistles can be achieved by appropriate warping of the time dimension. That is to say whistles with the same features in the same order come from the same dolphin even if things vary a bit otherwise in the time dimension. A trick which the authors say does not work with humans because a reduction to the fundamental frequency – or any other simple derivative of the complete spectrogram – is too reductive.

Whistles that are clever in that they are cerebrally produced, are an artefact of the social brain rather than a straightforward consequence of the chemical genes. They are like a word in that one still has the same word, despite variation of detail, despite noise. Robust in that sense. But not like a word in that they are a call sign, not a calling. It is not as if one dolphin can call another, can summon another by whistling his whistle.

So an interesting cul-de-sac in the evolution of words and names proper.

 PS 1: From reference 2 we have more elaborate charts. ‘Figure 1 [above left]. Social network of 17 adult males grouped in their second-order alliances. Only coefficients of association (CoAs) R0.2 are shown, as this reliably identifies second-order alliance partners, and males are color coded by alliance membership. The thickness of the lines indicates the strength of the dyadic social relationship, and alongside each male is a spectrogram of his signature whistle (sampling rate: 96 kHz; fast Fourier transform (FFT) length: 1,024; Hanning window function). See also Figure S1 [above right] for determination of alliance membership’.

PS 2: there seems to be a fair amount of academic controversy about all this. The dust does not appear to have settled.

References

Reference 1a: Dolphins learn the ‘names’ of their friends to form teams – a first in animal kingdom – Virginia Morell – 2021.

Reference 1b: https://www.sciencemag.org/news/2021/04/dolphins-learn-names-their-friends-form-teams-first-animal-kingdom.

Reference 2: Acoustic coordination by allied male dolphins in a cooperative context – Bronte L. Moore, Richard C. Connor, Simon J. Allen, Michael Krützen and Stephanie L. King – 2020.

Reference 3: Bottlenose dolphins retain individual vocal labels in multi-level alliances - King SL, Friedman WF, Allen SJ, Gerber L, Jensen FH, Wittwer S, Connor RC, Krutzen M. – 2018.

Reference 4: A quantitative measure of similarity for tursiops truncatus signature whistles – John R. Buck – 1993.

Reference 5: http://www.sharkbaydolphins.org/. ‘The famous dolphins of Shark Bay, Western Australia, have been studied since the early 1980s. Almost 40 years of scientific research into one of the world’s most fascinating animal populations has provided insight into their behaviour, social structure, genetics, communication and ecology, including the daily challenges they face to find mates and food, and to avoid enemies and predators. Shark Bay is a busy place for a dolphin, packed with friends and foes, collaborators and competitors. Vast seagrass meadows provide forage for turtles and dugongs, and a nursery for fish; shallow sand flats and mangroves are home to invertebrates, rays and small sharks; deeper channels support sponge gardens and rocky reefs, providing hunting grounds for sea snakes, large sharks and, of course, dolphins’.

Reference 6: https://theadopteddaughter.com/monkey-mia-shark-bay-western-australia/. The source of the opening snap of a viewing facility somewhere on Shark Bay. Another person of faith. They seem to get everywhere!