Dolphins

A bottlenose dolphin calf develops a distinctive frequency contour during its first year and then keeps it, largely unchanged, for the rest of its life. Other dolphins can tell whose it is. The obvious explanation is that they recognise the voice, in the way you recognise a friend on the telephone — and the experiment that matters is the one that removed that possibility.

Researchers synthesised the contour — the shape of the whistle in frequency and time — with every trace of the animal’s voice removed, and played it to its relatives. They responded anyway. What identifies the individual is an arbitrary learned pattern, which is a property a name has and a voice does not.

What has not been shown is a dolphin using another’s whistle to talk about it to a third dolphin. That is the difference between a signature and a name, and it is the whole of the gap between the evidence and the headline.

The genetic work is the interesting part, because it was used to rule genetics out. If sponging were inherited, spongers should be related through their nuclear genes; if it were about habitat, spongers should be found wherever the right seafloor is. Neither holds. What predicts sponging is descent through the mother’s line, which is what social learning looks like when written into a pedigree.

In the 1980s two dolphins were taught artificial languages — one of gestures, one of sounds — with a vocabulary of objects, actions and modifiers and a fixed word order. They were then given sentences they had never seen, including reversible ones where the same words in a different order mean something different. They got them right.

This is a real and impressive result about what a dolphin brain can parse. It is not evidence that dolphins have a language, and the distinction is comprehension versus production: these animals understood structured instructions and never produced a structured utterance. Nothing in natural dolphin communication has been shown to have this property.

The anatomy is strange enough to be worth stating plainly. A dolphin makes its clicks in the nasal passages, not the larynx. It focuses them through the melon, a fatty lens in the forehead, into a narrow beam pointed forward. And it does not hear the returning echoes through its ears in any ordinary sense: sound enters through fat-filled channels in the lower jaw and is conducted to the middle ear.

What comes back is not a picture. A trained dolphin can tell a cylinder with slightly thicker walls from one with thinner walls, and a water-filled target from an oil-filled one, at tens of metres. Sound passes into objects and returns altered by what is inside them, so echolocation reports material and internal structure — information vision simply does not carry.

In Shark Bay, male dolphins form stable pairs and trios that work together to herd individual females. Those small alliances then combine into larger groups that take females from other alliances and defend against the same. Keeping track of that requires holding two social maps at once: who your partners are, and which other groups your group works with.

It is worth being honest about what the alliances are for. This is coercive herding of females by cooperating males, and it sits awkwardly with the benign social intelligence dolphins are usually credited with. The cognitive achievement is real; the behaviour it supports is not gentle.

The wider society is fission–fusion: animals associate, separate and reassociate constantly, so a dolphin meets the same individuals repeatedly across decades in changing combinations. That is the condition under which a stable individual label — a signature whistle held unchanged for a lifetime — earns its keep.

Breathing in a dolphin is voluntary rather than automatic, so a fully unconscious dolphin would drown. The solution is to sleep one cerebral hemisphere at a time, with the eye opposite the sleeping half closed, and swap over — so the animal is never entirely asleep and never entirely awake.

Two things about this remain genuinely puzzling. REM sleep, near-universal in mammals and often tied to memory, is minimal or undetectable by the usual criteria in cetaceans. And newborn calves, along with their mothers, show almost no conventional sleep for the first weeks of life — an animal that swims continuously from birth, apparently without the rest every other mammal requires.

1. 1965

   First observation

   Signature whistles proposed

   Melba and David Caldwell noticed that individual captive dolphins each produced a distinctive, repeated whistle contour, and proposed that it functioned as an individual identifier.

2. 1984

   Landmark experiment

   Dolphins shown to parse taught sentences

   Two dolphins trained on artificial gestural and acoustic languages responded correctly to novel sentences, including reversible ones where word order determines meaning.

   Comprehension of sentences by bottlenosed dolphins

3. 1990

   Replication

   Whistles shown to be stable across a lifetime

   Recording individually known wild dolphins repeatedly over years established that signature whistle contours persist for at least a decade, and that calves develop their own rather than copying the mother.

   Signature whistles of free-ranging bottlenose dolphins Tursiops truncatus: stability and mother-offspring comparisons

4. 1992

   Modern discovery

   Nested alliances found in Shark Bay

   Long-term tracking of individually recognised males revealed alliances that themselves form alliances — a two-tier social structure otherwise known mainly from humans.

   Two levels of alliance formation among male bottlenose dolphins

5. 2006

   Landmark experiment

   The voice is stripped out, and recognition survives

   Wild dolphins responded to synthetic reproductions of a relative’s whistle contour with all voice characteristics removed, showing identity is carried by the learned pattern rather than by vocal timbre.

   Changes how the 1965 result reads

   The Caldwells’ proposal had an obvious alternative explanation that stood for forty years: dolphins might simply be recognising each other’s voices, as most social mammals do. Removing the voice entirely and finding recognition intact is what converted a plausible interpretation into a demonstrated one.

   Signature whistle shape conveys identity information to bottlenose dolphins

6. 2013

   Modern discovery

   Dolphins found to copy each other’s whistles

   Dolphins were shown to reproduce the signature whistles of close associates, and to do so most when separated from them — the nearest thing yet observed to addressing an individual by name.

   Bottlenose dolphins can use learned vocal labels to address each other

A dolphin breathes air through a blowhole on top of its head — a nostril that migrated backwards over evolutionary time — and it breathes voluntarily, one conscious decision at a time. That single fact explains a surprising amount, including why a dolphin cannot sleep the way a land mammal does and why anaesthesia is dangerous for one.

• No gills, and no ability to extract oxygen from water. A dolphin held underwater drowns.
• Teeth, in a single set that is never replaced — a dolphin that loses one does not grow another.
• Hair, briefly: calves are born with a few whiskers on the rostrum which are lost within weeks.
• No drinking. Fresh water comes from food and from metabolising fat, since drinking seawater would cost more water than it gained.
• Cannot survive on land: without the water’s support, body weight compresses the lungs and the animal overheats.

The jumping has more than one explanation and no single answer. Leaping is cheaper than swimming at speed — air offers far less resistance than water — so a travelling dolphin porpoising is saving energy. It also dislodges parasites, gives a look above the surface, and appears in social and play contexts where no practical function is obvious.

Riding the bow wave of a boat is the same economics. A vessel pushes a wall of water ahead of it, and a dolphin in that pressure field is carried along for very little effort — the same trick they use on the wave in front of a large whale, which long predates boats.

A bottlenose dolphin is pregnant for about twelve months and gives birth to a single calf, tail first — an arrangement that matters, because a calf emerging head first would have to hold its breath through the whole delivery. The mother, sometimes helped by another female, guides it to the surface for its first breath within seconds.

• Gestation around 12 months; a single calf, born tail first.
• Nursing for one to two years, on milk delivered by muscular contraction rather than suckling — a calf cannot form a seal underwater.
• Calves stay with their mothers for three to six years, learning foraging techniques that differ between families.
• Females typically calve every three to six years, which makes population recovery slow.
• Wild bottlenose dolphins commonly live 40 to 50 years, with females often outliving males.

The learning period is the part that connects to everything else on this page. Sponging — carrying a sponge as a tool while foraging — passes from mother to daughter over those years, which is why it runs in matrilines rather than spreading across a population. A dolphin calf is not simply growing; it is being taught a local way of making a living.

Captive lifespans have historically been shorter than wild ones, and comparisons remain contested because captive populations are small, unevenly aged and change with husbandry practice. NatureHQ records the wild figures and treats the captive comparison as an open question rather than a settled number.

Dolphins are whales. All dolphins are toothed whales, the killer whale is the largest dolphin, and the animals people call porpoises are a separate family with blunter heads, no beak and spade-shaped rather than conical teeth.

• Delphinidae — oceanic dolphins, around 40 species, including the killer whale and the bottlenose.
• Phocoenidae — porpoises. Smaller, beakless, spade-shaped teeth. Not dolphins.
• River dolphins — several unrelated families that arrived at a similar body separately; the Ganges and Amazon river dolphins are not close relatives of each other.

The confusion is worth clearing up because research findings do not transfer across these groups. A result about a bottlenose dolphin says nothing reliable about a harbour porpoise.

A dolphin appears to be smiling and cannot do otherwise. The upturned line of the mouth is fixed anatomy — the jaw and the melon give the face that shape whatever the animal is doing, and there are no facial muscles to move it. A dolphin in pain, in distress or dying looks exactly the same as one that is not. Almost everything people believe about dolphin temperament traces back to that accident of skull shape, and the belief has real consequences: captive animals in obvious distress have been read as content by visitors for decades.

The behaviour underneath is more interesting than either the friendly version or the corrective version that has replaced it in some quarters. Wild dolphins are curious, socially complex, and entirely capable of aggression. They kill harbour porpoises in some populations — repeatedly, with severe injuries, and not for food, which remains unexplained. Males form coalitions that coerce females. Infanticide has been documented. None of that makes them malicious; it makes them a large wild predator with a rich social life, which is exactly what they are.

Attacks on people are rare and are almost entirely associated with feeding or with lone habituated animals. A dolphin that has learned to associate people with food loses its wariness, and injuries follow — which is why feeding wild dolphins is illegal in many places. The stories of dolphins protecting swimmers from sharks are a different matter: some incidents are well attested, and there is no way to distinguish protection from a dolphin group mobbing a shark for its own reasons, with a person incidentally inside the circle. The more careful reading is that dolphins harass sharks, which they do, and that a swimmer sometimes benefits.

Bow-riding — the behaviour that puts dolphins in front of a moving ship — is the one that looks most like friendliness and is best explained without it. A moving hull pushes a pressure wave ahead of it, and a dolphin positioned in that wave is carried along with almost no effort. They did it with whales before there were ships. The dolphins riding a bow wave are getting a free ride, and whether they also enjoy it is not something a boat can tell you.

The pufferfish story is one of the most widely repeated claims about animal behaviour, and it rests on considerably less than its circulation suggests. Footage from a 2013 documentary showed young dolphins passing a pufferfish between them, mouthing it gently rather than eating it. The narration proposed that they were deliberately taking small doses of tetrodotoxin to get high, and that framing is what travelled.

What can be said: the behaviour was filmed, the fish was passed around, and it was not eaten. Tetrodotoxin is genuinely one of the most potent toxins known, and it is a nerve blocker rather than anything resembling a recreational drug — at low doses it produces numbness and paralysis, not euphoria, in every animal it has been studied in. No measurement of dose, of uptake, or of any physiological effect on the dolphins was taken. Dolphins also handle, toss and pass all sorts of objects, which is the ordinary explanation and the one the footage on its own supports.

NatureHQ records this as an observation of object play with an untested interpretation attached. It could be right. Nothing published establishes it, and a documentary hypothesis repeated for a decade does not become evidence by repetition.

The shark question is better grounded. Dolphins do attack sharks, ramming them in the gills and flanks, and groups have been recorded driving sharks away and occasionally killing smaller ones. They are also eaten by large sharks, frequently — bite scars are common on wild dolphins, and shark predation is a leading cause of calf mortality in some populations. The two facts sit together: a dolphin group can beat a shark and an individual dolphin usually cannot, which is why the behaviour is collective.

• Do dolphins use a signature whistle to refer to an absent individual — the last missing piece of the "name" claim?

  Why it matters: This is the single result that would make the word “name” defensible rather than an analogy, and popular coverage of dolphin communication already assumes it has been shown.

• How much information beyond identity does a whistle carry?

  Why it matters: If whistles carry emotional state, location or intent as well as identity, the signalling system is far richer than a set of individual labels.

• Why is sponging almost exclusively female?

  Why it matters: The sex bias is the strongest clue to why the tradition persists, and nothing currently separates foraging need from opportunity to learn.

• What does passing the mirror mark test actually indicate about a dolphin’s self-representation?

  Why it matters: The test is used across species as a proxy for self-awareness while what it measures remains disputed, so its results are routinely over-read.