For many of our readers, no memory of summers by the sea is complete without the odd sandwich-snatching seagull.

But has this most iconic of seaside stalwarts become a thing of the past?

Have seagulls turned their backs on the sea in favour of a cushy life in the city?

The question was sparked by a study recently published in the journal Bird Study, which tracked a colony of lesser black backed gulls breeding 30 km from the coast in The Netherlands.

These birds visited agricultural fields and freshwater sites. But they preferred refuse dumps. And of 710 recorded trips made by the gulls, just two were directed to the North Sea. Analyses of the birds' waste confirmed they had not eaten a single meal caught at sea. Yet the gulls were thriving.

So BBC Earth asked our audience on Facebook if seagulls have moved away from the sea?

And it turns out there are a few seagull sceptics in our midst.

Tony Kavanagh wrote: “wow, BBC calls it a seagull, might want to get an expert to proof-read before publishing,” while David Wiltshire followed this up with: “that's not a seagull - heck, there's no such thing.”

There isn't such a thing as a seagull

First, to address the seagull-truthers out there, the term seagull is a confusing one and technically not a true name. When we posed our question to Tony Whitehead, Public Affairs Manager of the UK-based Royal Society for the Protection of Birds (RSPB), his first response was ‘which do you mean?’.

“Seagulls are a massive family of birds. They’re really successful creatures, all scavengers with a global distribution.”

Peter Rock, urban gull expert and a Research Associate at the UK's University of Bristol, had a similar reaction.

“Despite the fact I use the word quite regularly, there isn't such a thing as a seagull,” he says.

To answer our question, we focused on the UK’s most common gulls: herring gulls (Larus argentatus) and lesser black back gulls (Larus fuscus). Found along the coast and in the countryside, both species have successfully moved into urban areas where herring gulls are found on the roofs of houses and lesser black back gulls on top of industrial and commercial buildings.

Rather than commenting on any fall in coastal gull populations, most readers noted a rise in city dwelling birds.

Philip L Meers took a friend to the seaside who commented “that he saw and heard far more gulls when we were at my home in Birmingham” and Amyv Wilson wrote there were “definitely more dumpster gulls than seagulls these days”.

Outside the UK, Mara Bingamon has noticed the appearance of gulls in southern Ohio, US over the last 15 years. And though Angel Norton of Wisconsin, US has never been near the sea, she has come into contact with many gulls. “In my experience seagulls tend to congregate in empty parking lots,” she adds.

Rock estimates urban gulls have been around for thousands of years, but they only began breeding on buildings after World War Two following the introduction of landfills on the outskirts of city centres.

Their numbers truly began to climb in the UK with the passing of the country's Clean Air Act in 1956, which prevented landfill operators from burning rubbish on site.

Urban gulls are taking over the world

“This was an open invitation to the gulls. They had a feeding bonanza,” says Rock.

Landfills may have encouraged gulls to nest in our cities, but with increasing anti-gull measures in place they aren’t the reason they have stuck around.

“Once urban populations start developing they realise it's actually quite a comfortable life,” says Rock.

In the past 35 years, the number of gulls nesting in British cities has increased sharply.

Since the last national census of seabirds in the UK was conducted in 2000 the number of urban gull colonies has more than doubled from 239 to 512, says Rock. Cities offer gulls a safe environment free from predators and disturbance, warmer temperatures than the countryside and street lighting to enable foraging at night.

The key to the urban gull’s success is not necessarily easy access to food, adds Whitehead, as tracking studies have shown that gulls continue to forage quite a long way from urban areas. Rather, their numbers are being bolstered by rooftop nesting space free from predators.

“Herring gulls in urban areas are doing incredibly well. They're producing more chicks each year so you're seeing a real boom in population,” says Whitehead.

Despite their incredible population growth, the number of herring and lesser black backed gulls in urban centres is only a small proportion of the total population found nesting on coastal cliffs, offshore islands, by lakes and on moors. It is at these natural sites that gulls are faring much worse.

Rock’s research over the years has shown that in most cases gulls hatched in town will not recruit into a wild colony and vice versa.

What has developed, according to Rock, are two distinct populations that, despite encountering each other on migrations, don't really mingle.

Rock reports that in the last 30 years, non-urban herring gulls have seen their numbers drop by 60 per cent, while lesser black back gulls have declined more than 30 per cent.

Whitehead says there are three major factors contributing to their decline; a lack of food (or food not being in the right place at the right time), disease and predation. The decline of the UK fishing fleet has also played its part.

“Bycatch isn't available in the quantity it used to be and we know in other places around the world this is affecting the seagull population.”

Though Whitehead points out that the presence of trawlers may have artificially inflated population numbers in the first place.

So have seagulls abandoned the sea?

Rock says no. The majority of gulls are still nesting in natural sites and there are plenty of urban gulls to be found in towns and cities by the sea.

“They all move around. Usually herring gulls disperse off to the coast even if they have been breeding inland. It may well be that people who have been used to going to the seaside with hordes of seagulls have noticed that there is some decline,” says Rock.

Ongoing GPS tracking studies being conducted by Rock and other researchers around the world will continue to shed light on where city-living birds are spending their time – are they true seagulls, part-time seagulls or full time citygulls?

“Urban gulls are taking over the world. It may be that some point in the future urban gulls outnumber rural gulls,” says Rock.

Kara Segedin is BBC Earth's social media editor. She is @ksegedin on Twitter.

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