Dolphins often seem to want to befriend us - do they know something we don't?

Why, despite our frequent cruelty to them, do dolphins seem to actively seek out encounters with humans? Are they trying to tell us something? Do they think we have something in common? In her new book, Susan Casey explains all

By loyal appointment: Fungie the bottlenose dolphin has been a local attraction in Dingle since 1983 (Jeannine Masset and Rudi Schamhart)

You'll have heard of Fungie, a male bottlenose who has forsaken the open sea to live inside the harbour mouth of Dingle in Ireland, a placid, shallowish inlet bordered by low verdant hills that are speckled with sheep.

According to local legend, he has been swimming around in this area, not much bigger than a few city blocks, since October 1983.

It doesn't seem like an auspicious place for a dolphin to settle. Though the bay is sheltered from snarlier North Atlantic conditions – churning seas, huffing winds – dolphins are well equipped for these things and seem to revel in the action: surfing down the faces of waves, leaping through the wakes of ships, playing in the maelstrom. By comparison, the Dingle harbour is a pond. Nor could it be mistaken for a marine sanctuary: it was known in the past for its abundant reservoirs of rubbish. So what was a full-grown bottlenose with an entire ocean at his disposal doing in this fish tank? And where was his pod? Being part of a pod means protection, hunting success, society, sex, kin – the fundamentals of dolphin existence. A solitary dolphin is like a floating oxymoron. So how did this one survive?

The tales of Fungie the loner dolphin seem improbable. But surprisingly, there are others like him. Scientists don't know why it happens, but tales of dolphins befriending humans reach far back into history. Aristotle wrote offhandedly about dolphins' "passionate attachment to boys", as if everyone just knew this as a fact. In the year AD 77, Pliny the Elder recounted the story of a dolphin named Simo who formed a bond with a boy who fed him bits of bread, giving him rides in return:

"This happened for several years, until the boy happened to fall ill of some malady and died. The dolphin, however, still came to the spot as usual, with a sorrowful air and manifesting every sign of deep affliction, until at last, a thing of which no one felt the slightest doubt, he died purely of sorrow and regret."

When you consider how risky it is for dolphins to spend time in close proximity to people, it is all the more intriguing that so many human-dolphin stories have similar themes: dolphin seeks out man, dolphin wants to play with man, dolphin assists man, dolphin rescues man. If dolphins didn't already have such a well-established reputation for showing up like Superman in the third act, it would be impossible to put their behaviour into context. But there are centuries and even millennia of tales of their generosity towards the awkward two-legged creatures they encounter who are so out of their element.

In the book Beautiful Minds, biologist Maddalena Bearzi recalls tailing a pod of bottlenoses on one grim, foggy morning along the coast of Los Angeles, as they herded a huge school of sardines. If there's anything that commands a dolphin's attention it is a mother lode of fish, so Bearzi was surprised when one suddenly broke away from feeding and headed out to sea at top speed. The rest of the pod followed; so did Bearzi and her crew. The dolphins arrowed about three miles offshore and then they stopped, arranging themselves in a circle. In the centre, the scientists were shocked to see a girl's body floating.

Tales like this are remarkably common and surfers, in particular, seem to benefit from dolphin intervention. When Todd Endris was bitten three times by a great white shark near Monterey, California, dolphins drove off the marauder, formed a ring around Endris, and escorted him to the beach. Australian Dave Rastovich, straddling his board waiting for a wave, was astonished to watch a dolphin hurtle itself at a shark that was torpedoing towards him, sending it fleeing.

Leap of faith: a spinner dolphin off the Kona coast, Hawaii (Rennio Malfredi)

What to make of these stories? One point worth noting is that dolphins often behave towards us in the same ways they do towards one another. In the dolphins' nomadic undersea world, solitude equals vulnerability, so a lone human in the water must seem to them direly in need of assistance. But their consideration of us isn't limited to emergency situations: at the Tangalooma Island Resort in Australia, where wild bottlenoses are regularly fed fish by people standing in the shallows, biologists have documented – on 23 occasions – the dolphins reciprocating, swimming up to offer freshly caught tuna, eels, and octopi as gifts.

In other words, dolphins do not always differentiate between us and them. Maybe that was why Fungie had made his home among the residents of Dingle. To him, perhaps, they were just a slightly peculiar-looking pod.

I drove down to Dingle from Dublin, winding through green and peaceful country, through bustling little cities and quaint little towns, then parked my car near the town square and got out to take a look around. Behind a life-size statue of Fungie there was a stone building that looked like a harbourmaster's office; its windows were plastered with Fungie posters and advertisements and press clippings. One announced that "fun-loving Fungie the dolphin has somersaulted into the record books... as The Most Loyal Animal on the Planet!"

To win this title, I read, Fungie had outdone a Risso's dolphin named Pelorus Jack who spent 24 years, from 1888 to 1912, escorting ships through New Zealand's tricky Cook Strait. Before the dolphin stepped in, these waters had hosted a number of New Zealand's worst maritime disasters. Pelorus Jack's job, as he performed it, was to guide boats to a safe crossing. Usually he would just materialise at the bow; if he didn't, captains would often stall their vessels and wait.

During his tenure, Pelorus Jack's reputation spread far. Songs were written about him. Sometimes he appeared in gossip columns. Rudyard Kipling and Mark Twain both watched him in action – as I now would Fungie.

A Bronze Age-era fresco in the Palace of Knossos, Crete (Rennio Malfredi)

The next morning I bought a ticket for the Lady Avalon, a sturdy blue and white trawler, for a tour of Dingle Bay, where a dinghy, a white Zodiac, and a trio of sailboats circled.

"Anyone see him anywhere?" The captain, a man named Jimmy Flannery Sr, stuck his head out of the wheelhouse. No one had, but not for lack of looking. Then, suddenly, from our stern, a lady in a yellow slicker yelled: "There he is! Oh my god! I saw him!"

With a whooshing outbreath the dolphin had surfaced, and he was close enough that I could see his distinctive, gnarled face. Fungie looked pugilistic, and disconcertingly huge, with white markings around his chin like an old man's whiskers. He bore noticeable scars: his beak was roughed-up at the tip and his tail was missing a divot. On his throat he had the dolphin equivalent of deep wrinkles. Still, this was a big, tough bottlenose. I had read that Fungie was 12ft long and weighed 700lbs, but those numbers are low. My first thought was that the Most Loyal Animal on the Planet could knock someone's lights out if he wanted to.

Watching the dolphin, I felt a palpable glee emanating from him. No wonder the town had claimed him as their own – he was a skilled entertainer. He made perfect aerial arcs, walked on his tail and at one point swam along on his back, clapping his pectoral fins.

Observing him, I found myself wondering if Fungie's past might have included a stint in captivity; if, back in the day, he had lived in a sea pen and somehow escaped. It had been known to happen, especially during storms. Unfortunately, they don't always know where to go or what to do with their sudden freedom, and so they seek out what they're accustomed to: people. Could Fungie be a refugee? We can only guess. But back at the docks, I decided to share my theory, with the skipper. "It seems like someone must have trained him," I said. "Do you know if they did?"

Flannery, who had been smiling pleasantly enough before I said this, turned and stared at me hard. A shadow passed fast over his face, darkening it like a thundercloud.

"Not at all," he said curtly, turning away dismissively. "He is a totally wild animal."

Wild? Dolly in France and Paquito in the Basque country; Egypt's Olin, who befriended a tribe of Bedouins in the Gulf of Aqaba; Charlie-Bubbles from Newfoundland; Springer from Seattle and Scar from New Zealand; Chas, who loved a particular buoy in the Thames – these and so many other solitary dolphins have made themselves known to us. And that is usually where the problems begin. The inevitable unruly relationship between a solitary dolphin and the people who want to see him vexes biologists, who fear – correctly – that these encounters will end badly for the dolphin.

Their biggest threat, by far, is propellers, which seem as alluring as they are deadly: scientists have heard dolphins playfully mimicking the sounds of motorboat engines underwater, the way children do with their favourite toy trucks. Wilma and Echo, orphan belugas from Nova Scotia, both died from propeller strikes, but not before charming thousands of people, gliding up to sightseeing boats to let passengers stroke their skin.

Jet, a bottlenose from the Isle of Wight, had his tail lopped off by a propeller and bled to death. Freddie, a bottlenose from Northumberland, whose companion had swallowed a plastic bag and washed up dead on the beach, liked to swim upside down beneath motorised dinghies; once again, it was a propeller that got him.

But propellers are only one hazard among many. To read through a list of friendly wild dolphins who have met violent and untimely ends is to read a list of appalling human behaviour. Over in Israel, Dobbie, a bottlenose who liked to play with the air bubbles from scuba divers, washed up full of bullet holes.

Another, called "The Costa Rican", fell in love with a local dog which he would meet every day, pushed children around in a canoe, and let people ride on his back. When he became entangled in a fisherman's net, he waited calmly for help to arrive. Instead, the fisherman gaffed him and dragged his body on to the beach.

However, surrounded by people who want to swim with them, touch them and grab their fins, dolphins can become aggressive themselves. Lone dolphins, removed from everything familiar and confused by their new acquaintances, have been known to pin snorkellers to the seafloor, break arms, ribs and noses with their beaks, make amorous advances and club swimmers with their tails. Far from rescuing people, if a dolphin is sufficiently riled-up, he might prevent them from exiting the water, or push them farther out to sea.

Take the case of Lakeshore Estates, a gated waterfront community in Slidell, Louisiana, which became host to a hostile resident bottlenose, known impersonally as "The Dolphin".

During Hurricane Katrina the young male had become separated from his pod, and ended up alone in a brackish canal in the middle of the suburb. In the seven years since his arrival, The Dolphin had done quite a bit of damage, and his behaviour was becoming increasingly ornery. In a flurry of activity he'd bitten several people – including one girl he'd attempted to drag away from shore by the ankle – chased swimmers out of the water, snapped his jaws at kayakers and body-slammed dinghies.

Protection: A pod of dolphins in Hawaii (Rennio Malfredi)

Concerned about his surliness, residents held a community meeting with government biologists and officials, 60 Slidell locals attending, along with a pair of sheriffs.

"Why can't we remove it?" complained a thin man with a bushy white moustache. "You know, if you put it in an aquarium, the problem is solved."

"Or maybe they should find him a girlfriend," suggested a woman in a white trouser suit and red lipstick. (It was true that The Dolphin often swam around with an erection, which he rubbed against boats.)

"The problem is the people," a burly Cajun wearing a Coast Guard baseball cap shot back. The biologists agreed: the best thing the community could do for The Dolphin was to steer clear of him. No more racing him on Jet Skis. No more following him around to take smartphone videos of his penis. The less human interaction he had, the more likely his bad behaviour would stop.

"You know, he's just like us," said another man, whose home and business had been dashed by the hurricane.

"He lost everything, but he's put it behind him and is fine. He's a survivor. People just have to leave him alone now."

The one thing we know for sure about lone friendly dolphins is that we are likely to meet more of them. Across the world, their society and ours are inevitably colliding. Even if dolphins manage to evade our web of fishing nets and longlines, they still contend with relentless pollution, oil spills, habitat destruction, food depletion, a barrage of brain-jangling noise – the list goes on. Of course we'll find them among us: they have nowhere else to go.

In so many ways, I came to realise, Dingle is a best-case scenario for a podless dolphin. There is no way to watch Fungie and doubt that he is having fun. He hunts for his own food. He is savvy enough to avoid propellers and dodge assholes. He has bonded with people but he's not completely isolated from his own species. (Lately, he has been seen gallivanting with two females.) In all situations the town protects his interests. And if The Most Loyal Animal on the Planet ever decides that he has been loyal to Dingle for long enough, he is free to leave as he pleases.

Obviously, the town is praying that never happens. What's good for Fungie is good for them. But as I drove away from Dingle, the bay shining behind me, I gave my own silent thanks to the people who had cared enough to protect a lone dolphin, the town with a Fungie-shaped space in its heart.

This is an edited extract from 'Voices in the Ocean' by Susan Casey (£16.99, Oneworld)