“They sent you all this way to ask about a seagull?” The taxi driver looked at me in the mirror. In his eyes, I saw confusion, maybe a little fear. I smiled wearily. Not now, I thought. Not him, too. No more talk of seagulls. It had been a long couple of days. I was so nearly out of Saigon I could hear the rotor blades thumping above.

By Saigon, of course, I mean Bridport, west Dorset, a seaside market town of charity shops, estate agents and bad local art galleries. By rotor blades, I mean seagulls. For the past 36 hours I had thought about little else. If you gaze at the seagull long enough, I learned, it gazes back at you. You wonder whether it has a demonic quality. A seagull will do strange things to a man.

'Killer' seagulls top the pecking order for a media frenzy Read more

I suppose it’s fair. After all, I only went because someone had done strange things to a seagull. In recent months, the war between humans and seagulls has seen a dramatic escalation in violence. In Cornwall, diving gulls attacked a 66-year-old woman, who needed hospital treatment, and “savaged” a four-year-old boy, whose finger was badly hurt. They killed a pet dog. They flipped over a beloved tortoise and ate it from the soft side, like a dressed crab. David Cameron called for a “big conversation” about them, one of his highest settings of inaction. In George Osborne’s spring budget this year, £250,000 was allocated for the seagull issue, but the money was quietly taken off the table after the general election.

The struggle continues. This week, it was reported that a seagull had swallowed a starling whole after smashing it to death on a roof. There were pictures. Patrick Barkham wrote a Guardian column urging us not to think of them as terrorists. At last, seagulls are getting the attention they deserve.

But none of the other attacks had the mystery of the Bridport case. According to news reports, last Friday a seagull had been dumped outside Bridport police station, just alive but in a terrible state. The RSPCA suspected poisoning, and had taken the bird into its care. The gull had been tending its chick, who was now nowhere to be seen.

Against a background of growing seagull insurgence, was this the first step in a vigilante fightback? Or a mafia-style warning: GSH, grievous seagull harm, pour encourager les autres. And why Bridport? It has seagulls, but so do all seaside towns. What it does have to itself, however, is Broadchurch, the detective TV series starring David Tennant and Olivia Colman, set in a fictional town but filmed in Bridport. This extra layer of intrigue seemed to rule out seagull-on-seagull crime.

My priority was the bird itself. If it was on the mend and receiving visitors, it might provide valuable clues about its attacker. I spoke to Stephen Powell, the local RSPCA welfare officer, who had rushed to the scene.

“It was in a bad way,” he said. “I’d never seen a seagull like that. Its neck was twisted 180 degrees, it couldn’t stand up, it had regurgitated some of its food and some blood.” He took the seagull and drove it to the West Hatch animal centre, in Taunton, but it was too late. “Sadly the seagull was dead before we arrived.” I deflated. I had allowed myself to daydream about helping to nurse the seagull back to health; perhaps watching it take its first tentative steps back into the world. “Sorry not to be more help,” he added.

On the contrary, things had just got interesting. My assault was now a murder investigation. Next up was the police station. With a kind of crushing inevitably, it was shut. Crime never stops, except in Dorset, apparently, where it stops on Mondays, Wednesdays, Fridays and Sundays. A young seagull looked down on me from the roof, unbowed by the recent catastrophe. My own peregrinations would have to suffice.

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Across the road was an American-themed diner, decorated in Confederate flags and pictures of Elvis Presley, with wide windows that gave a full view of the front of the police station. I asked Tony Marraffa, the owner, whether he’d seen any suspicious gull behaviour.

“I didn’t see anything, and I’d have known about it if there had been a seagull outside the front. Most of them don’t survive, anyway; they end up little grey things squashed on the road.”

I thanked him for his time and walked the two miles or so down to West Bay, a gorgeous beach with a sliver of mustard-coloured sand running below ancient cliffs. It is the main local attraction, the backdrop to the Broadchurch posters. At the mouth of the river Brit is a small harbour ringed by fish-and-chip shacks. This was it: Seagull Shangri-La. There were hundreds of them. Some looped like Messerschmitts in the coastal air, some stood on the harbour. Others bobbed in the water, resting before the next assault.

“They’re noisy, they’re smelly, they wake up early, they follow you around, they attack other birds,” said Amy Sibley, a waitress in a restaurant called – I accept some of you won’t believe this, and invite you to Google it – Seagulls. “I was on the roof the other day and saw them kill a racing pigeon. We found a leg with the tag on it, and had to call up the owner to tell him we’d found a bit of his bird.”

Facebook Twitter Pinterest A local faces off with a seagull in Bridport. Photograph: Mark Pas

“We’ve been here 17 years and they’re worse than ever,” agreed Lucy Blake in the No 8 fish and chips stall. “They’ve been a real menace for our customers. But you can’t do anything about it. They’re protected.”

This was a common refrain. Like all wild birds, seagulls are protected by the 1981 Wildlife and Countryside Act. They can only be culled in special circumstances, with permission of the Department for Environment, Food and Rural Affairs. But perhaps there was another way of dealing with the problem? Lucy’s husband, Barry, certainly seemed to think so. “Nobody likes to see them hurt, but you could shake a few eggs at the start of the year so fewer of them hatched,” he said. It’s probably worth clarifying that Barry’s solution – and interfering with nests more generally – is firmly proscribed by the law. Still, the approach has been tried in Devizes, Wiltshire, where a seagull siege prompted the ruthless destruction of 600 eggs. It proved controversial, to say the least. “There’ll be those that don’t like it,” Barry went on, “but there always is. You’re never going to please everyone.” Sadly neither of them knew anything about the poisoning.

Everyone had a story about a vicious attack: ice-creams taken from hands, sausages stolen from barbecues, but I’d never experienced one myself. I took some of Lucy and Barry’s cod and chips and ate them slowly, with the paper open on my lap, an irresistible punnet of starchy entrapment. A large specimen landed in front of me but kept a respectful distance. Up close, they are not bad looking: white breasts, grey wings, black tails, yellow beaks protruding like the prow of a trireme from their shapely heads. There’s a certain nobility to their swagger.

Also, don’t we loathe seagulls for many of the reasons we loathe ourselves? They are urbanising. They are too noisy. They make too much mess. They prefer to eat chips and other rubbish (often literal rubbish) than fresh herring. But they have also been forced inland because of human overfishing. They congregate at the seaside, just like our other bogeymen: immigrants, for the far right, and the far right, for everyone else. In that context, seagulls start to look like Ukip-voting miniature pterodactyls. “Psycho seagulls keep out illegals”, as the Star’s headline put it on Wednesday, after reports that the birds were dive-bombing a camp near Calais.

Yet they are also intelligent and resourceful, and have been shown to use tools. They travel widely and thrive wherever they go. They are mongrel species, happily cross-breeding to make identification very difficult. They have increased in nuisance value even as their overall marine numbers have declined, which means that they are getting more efficient. Seagulls are humans, at our best and our worst.

Facebook Twitter Pinterest PC Scott McGregor ready to apprehend the culprits. Photograph: Mark Passmore/Apex

I was startled from this reverie by an older woman walking past. She pointed at a tiny brown bird by my feet, looking hopefully up at the chips. “He’s been ever so patient,” she said. “They’re all right when they’re that size, aren’t they?” She was right. How much of our anti-seagull feeling is a simple accident of their largeness? I tossed a chip to the little guy. You can probably guess what happened next. A honking great seagull, like a set of weaponised bagpipes, plopped down and gobbled it up.

I had a where and when for my seagull murder, and a surfeit of motive, but I still needed a suspect. In the evening I went to a bar and asked the locals whether they knew anything about the crime. Their laughter suggested that perhaps the attack wasn’t as big a deal in Bridport as it was in central London. The band offered to claim responsibility if I gave them a plug. “Exterminate all the brutes!” suggested a young man in a flat cap. In the circumstances, the Heart of Darkness reference did not seem totally inappropriate.

Later I lay awake in my B&B, listening to the seagulls, trying to work out what sound they were making. A squawk? Shriek? Cry? Wail? What word are they calling to each other? Craaawwlll? Xoiiahhh? Eighhhh? Staring at the ceiling, I worked it out: they were saying “seagull”. “SEAGULLSEAGULLSEAGULL.” It had been a long seagull day.

Morning came. The police station was open. On the road outside was a squashed seagull. “Oh no,” said PC Alison Gale, who was on the front desk. “I had been feeding him, little bits of bread soaked in water. Maybe it was his first flight.” From a policewoman, this seemed a bold contradiction of the general advice not to feed the seagulls that I had seen plastered all over town, but I said nothing. I was here to meet PC Scott McGregor, the man who had found the body.

“Thank you for taking the time to follow this up,” he said, offering a hand. “It was quite an important story, I felt.” With his calm professional manner, he reminded me of Simon Pegg’s character in Hot Fuzz, the young policeman sent to a small village, whose competence is wasted on the cases he has to deal with. He showed me into a brown interrogation room, where we sat across a plain desk: “It’ll be quiet in here.” I confessed that I’d always imagined my first meeting in one of these rooms would be in different circumstances.

Facebook Twitter Pinterest These guys seemed like they might know something. Photograph: Mark Passmore/Apex

“Contrary to the early reports, the bird was not found in the front of the station, but the rear yard.” Hang on, so it wasn’t a mafia-style revenge killing at all? “The inspector indicated that poisoning was probable. We are waiting on the toxicology reports to see whether it was an artificial poison, or a natural poisoning, which can occur from botulism or salmonella.” Stephen Powell, the RSPCA man, confirmed that salmonella was a likely explanation. For some reason, the tabloid reports about the seagull had left this out.

Journalistic experience told me that a seagull killed by salmonella behind a police station might not lead the week’s agenda as I had hoped. But McGregor wasn’t finished.

“Sadly we’re no closer to identifying any suspects. But what we have found since is another discarded, dead adult in near proximity, in a public bin, within 100 yards of the station.”

A second (seagull) body! I could have kissed him. “Whether it’s had a natural death we don’t know, because it’s the carcass of a dead bird at this point. There’s nothing to indicate whether it’s linked to the first death, but it seems to me to be too much of a coincidence.”

“One’s an accident,” I said, eager for him not to underestimate the significance of the second dead seagull, and to keep on the trail. “Two’s a coincidence. But three ...”

“I’m not familiar with that adage,” he replied. “But once bitten, twice shy, you know? And there’s no smoke without fire.”

Seagulls are not terrorists. This war is a bad idea | Patrick Barkham Read more

He smiled. I smiled back, but I wasn’t sure if I did know. Still, I had my second body. “It indicates that perhaps it wasn’t just a one-off,” said McGregor. “But we don’t know whether it’s a situation born out of a deliberate act.”

The driver dropped me off at nearby Crewkerne station, still chuckling to himself. As I waited for the train I keep thinking about the most famous seagull-related quotation of all, from the footballer Eric Cantona. “When seagulls follow the trawler,” he said at a press conference in 1995, “it is because they think sardines will be thrown into the sea.”

Except in that analogy, the seagulls were journalists, waiting for his gnomic utterances. Wasn’t that exactly what I was doing, hunting these scraps of a seagull murder case? Journalists are seagulls. But what does that make you, the reader, hunting for scraps in seagull story? That’s right: also a seagull. This war is only just beginning, and we need to remember: really, we are all seagulls.

• This article was amended on 27 July 2015 to clarify that the writer was dropped off at Crewkerne station.

