From a gull's eye view, our cities and towns are a series of rooftop islands surrounded by steep cliffs. Nesting there brings a number of advantages – it helps to keep them safe as fewer predators tend to prowl around human architecture. There is also often no shortage of food on the streets below. As a result, urban gull colonies are taking off in Europe, and elsewhere.
But like many other species that have adopted urban areas as their homes – rats, pigeons, foxes – gulls have something of an image problem. "Even my birdwatching friends used to say, why do you want to study gulls. They are not even birds," says Peter Rock, a leading urban gull expert in Bristol, UK, who has studied the two most common urban gull species there for decades: herring gulls and lesser black-backed gulls. The tabloid press in the UK has depicted gulls as public enemies for incidents of birds dive-bombing pedestrians, either to defend their young or to snatch meals straight from the hands of unwary tourists. Their relentless noise and the mess they create has also drawn much ire from the local humans who live alongside them.
Gulls have been residents of cities and towns for decades. The birds were first recorded to be nesting in Bristol, for example, in 1972. Rock, who is also a member of the international Gull Research Organisation, recalls that in 1980, when he was first starting out studying the birds, there were around 100 pairs in the city. Now, he estimates there are 2,500 pairs, with 2,900 pairs in nearby Gloucester and 3,200 pairs in Cardiff.
Even cities far inland are now home to gulls. St Paul in Minnesota, hundreds of miles from the Great Lakes, is home to gulls, as is Minsk in Belarus, which is hundreds of miles from the Baltic.
Discarded leftovers and dropped takeaways provide gulls with easy pickings on our city streets (Credit: Robin Utrecht/Getty Images)
Once large gulls start to nest in urban areas, their colony sizes inevitably rise. The proportion of British urban sites with more than 100 nests of large gulls has increased by about 4% every 10 years between 1939 to 2000, notes John Coulson, a former professor of zoology at Durham University, in his seminal book, Gulls. In 2000, 15% of herring gull nesting sites in the UK were in urban areas, and experts say that number has likely increased since.
So, what is it that is drawing these birds in growing numbers to our towns and cities? And should they now be classified as an urban species alongside rats, pigeons, foxes and raccoons?
The first record of herring gulls nesting on a building in England was possibly on an old mill in Cornwall in 1909. There was no major expansion during the first half of the 20th Century, but with the landmark 1956 Clean Air Act, inland gull colonies began to increase, says Rock. Part of the reason for this was because landfill operators could no longer burn rubbish, instead covering it with soil each day.
"The gulls were quick to take advantage of this feeding bonanza," says Rock. By foraging for discarded food on landfill sites, urban nesters were able to raise more chicks, and more fledglings survived. The population shot upwards. This was not just a UK phenomenon. "A landfill in Portugal I used to go to had 20,000 gulls," recalls Rock – the large open area with plentiful food was perfect for the birds.
Industrialised fishing practices meant the natural food sources of the birds were being depleted while their nesting sites were often being disturbed
Alongside this another force was at play. Industrialised fishing practices meant the natural food sources of the birds were being depleted while their nesting sites were often being disturbed by human activity.
In the UK this led herring gulls and lesser black-backed gulls being listed as of conservation concern in the wild. But the birds were able to deploy their high avian intelligence, long lives and opportunistic nature to find a new habitat to thrive within – our cities.
According to ornithologist Irina Samusenko at the National Academy of Sciences of Belarus, rooftop colonies in of gulls started in Minsk at the end of the 1990s. Today, there are 5,000 to 6,000 pairs of large white-headed gulls, often on flat stone-gravel roofs of industrial buildings. There are also up to 3,000 pairs of black-headed gulls, and 1,000 common gulls. "There has been a significant increase in gull numbers in the Minsk area," says Samusenko, largely due to a decline in natural habitats such as lakes in the area and a corresponding increase in rooftop nesting sites.
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In Italy, gulls first nested in Rome in 1971, and then colonised Venice, Trieste and Naples. Elsewhere, such as on the Wadden Islands off the coast of the Netherlands, one lesser black-backed gull has been tracked routinely making a 80km (50-mile) trip to Amsterdam, according to research by Judy Shamoun-Baranes, ecologist at the University of Amsterdam.
"People are noticing more gulls in cities," she says. "It is possible they are increasing."
Many human residents of towns and cities are not keen on their new winged neighbours (Credit: Chris Putnam/Barcroft Media/Getty Images)
While gulls in Europe seem to have already adopted urban life, there are signs the birds are doing the same in the US too. Herring gulls can already be found nesting on buildings near the Great Lakes in the US and also on buildings in coastal cities like New York City and Portland, in Maine.
Lesley Thorne, a seabird ecologist at Stony Brook University, is investigating mixed colonies of American herring gulls and great black-blacked gulls on Long Island, Tuckernuck island and New York City.
"The gulls are smart. It is hard to catch them. Once you do, catching them again is even harder," she says. The powerful great black-backed gulls, the largest gull species, has a wingspan of over 1.5m (5ft) and mostly feed offshore. The herring gulls on Tuckernuck feed mostly at sea, but do visit landfills on land too. Those nesting on islands in Jamaica Bay, just south of Brooklyn, take advantage of more processed human food from restaurant waste while herring gulls nest on buildings in the area.
Much of the birds' success in cities is due to their long lives, which allows the birds to build up an extensive memory of where and how to find food. Unlike garden songbirds (which generally live 3-5 years), gulls can live decades and accumulate valuable experience. The oldest bird studied by Rock was a lesser black-backed gull fitted with a leg ring on a rooftop close to Bristol Bridge in 1989, which lived for 28 years. The gull decided to stay for his final days in the sunshine near Malaga, in Spain, laughs Rock. The European record for lesser black-backed gulls is 34 years of age.
The benefit of this long life, is that older gulls know all the tricks. "A wise gull knows everything about food within its home range," says Rock. The venerable lesser black-backed gull he had been following had frequented the Gloucester landfill for many years and when the landfill shut he found other means.
Gulls have large brains that make them able to adapt quickly to the challenges and fast changing environment of urban areas
Closing landfills is little in the way of a barrier to urban gulls. Outside Rome, the closure of the Malagrotta landfill in 2013 was "likely decisive in making them move more steadily inside the city", says Valeria Jennings, an ornithologist at the scientific association Ornis Italica. She is investigating why the city is benefiting gulls and what they are eating.
Gulls have large brains that make them able to adapt quickly to the challenges and fast changing environment of urban areas. They are also extremely intelligent – there are reports of them dropping shellfish on to rocks to break them open or fishing by using pieces of bread as bait to tempt fish to the surface.
Other research suggests gulls also have a keen sense of smell and that they can detect airborne odours over long distances, helping them to navigate as they migrate. With such an attuned sense of smell, it seems likely they can also use it track down sources of food.
And while rubbish tips are no longer such expansive buffets for gulls – recycling and composting have reduced food waste – gulls can still find plenty to eat elsewhere in our cities and beyond. So good are they at finding food, that researchers in Spain suggest that monitoring gull movements could allow authorities identify illegal dumping sites.
Research using GPS trackers on urban less-black backed gulls suggests that a sense of timing is crucial for gull success.
High ledges and windowsills of tall buildings in cities make perfect nesting sites for gulls as they offer protection from predators (Credit: Alamy)
Anouk Spelt, a behavioural ecologist at Bristol University attached GPS tags to around a dozen of the birds in Bristol city centre and tracked their movements each day. "They went to specific schools at breaktime and then sneakily hang around looking at the kids," says Spelt. A few also turned up for the opening school bell. Other gulls arrived at the same time each afternoon at a collection point where material for composting was piled up, picking from a pile of food scraps.
In the marine environment, gulls have to time their arrival to a feeding area with the tides and seasonal changes in food abundance. Our own daily lives follow similar regular patterns as shops open and close, schools have breaks in lessons and revellers leave bars at the end of the night.
"Gulls know when to follow the tides in Bristol and now they are able to match the temporal patterns that we follow," says Spelt.
Attaching GPS tags to such attentive creatures, however, is not a straightforward task in itself. Spelt says she has to swap between types of traps if she wants to catch gulls on the same rooftop as the birds watch and learn. "We need different cages to catch them," says Spelt.
Some gulls also appear to have learned to associate human behaviour with an easy meal. They will preferentially peck at food that they have seen been handled by a human – perhaps picking up cues about the quality of the food from humans. But while the birds themselves are clearly watching us as we are snacking, they don't like to be watched themselves. Herring gulls will retreat far sooner from a human staring directly at them than if the person is staring at the ground.
They are intrinsically beautiful birds and people have a grudging respect for them - Louise Blight
Spelt has discovered that the gulls she has been studying spend two-thirds of their time in suburban and urban areas, and the remainder in the surrounding countryside but not the seaside. After a downpour, for example, they fly to parks and farmland to feed on earthworms emerging from wet soil. Spelt also noticed her tracked gulls zig-zagging across farm fields. "The gulls walk behind tractors and ploughs, and eat invertebrates that pop up," she explains. The birds will also snatch up frogs, mice or anything else that gets disturbed.
"They eat lots of different types of food and can fly far at relatively low cost," says Spelt. Black-headed gulls have been found to fly around 18km (11 miles) on average as they forage for food when in their natural habitats. The furthest point Spelt's gulls foraged was 87km (54 miles), though most foraged within the city limits of 4km (2.5 miles). "They seem to stay closer to the city as they spend more time in urban area," she says.
But the gulls also have some less than savoury habits. Spelt followed one gull to a waste treatment plant, where it joined 20 birds to swoop down to pick sweetcorn from sewage water.
"You will see individual birds going to particular places that they know well," says Rock.
Gulls have made themselves at home in cities that are far from the sea, such as Birmingham, England, where this bird was seen in a shopping centre (Credit: Mike Kemp/Getty Images)
In Barcelona, yellow-legged gulls have been found to engage in both predatory and opportunistic feeding behaviour with fish, human garbage city pigeons and parakeets found in the stomach contents of their chicks.
Gull tracking in Rome has also revealed that urban areas provide far more than just food for the birds. Jennings has found while the gulls take long foraging trips inland to some landfills, and sometimes to the open sea, they also fly 30km to a quarry with freshwater to drink and bath. "Gulls mostly use the city as a dormitory and nursery, which is close to abundant food sources, instead of relying on tourists or garbage in the city centre," says Jennings.
Urban gulls also lay eggs slightly earlier than their country cousins, according to observations by Rock. He says because cities are generally warmer – a phenomenon known as the heat island effect – it triggers the birds to lay earlier, which then gives the adults more time to provision for themselves before they moult their flight feathers at the end of the summer. A Canadian study found higher fledgling success in urban gulls in Vancouver compared to their rural counterparts, with less predation.
In San Francisco, Western and California gulls have been found to fly 40km (25 miles) to visit a compositing site for food scraps from the city's restaurants, says Scott Shaffer, associate professor of biology at San Jose State University. He tracked one gull that twice hitched a ride in a garbage truck for 120km (75 miles). But Shaffer says neither gull species is nesting in urban areas yet, but he has heard of a small colony of Western gulls nesting on a store in Santa Cruz, with an ocean view.
Studies have shown that gulls prefer food that has been touched by humans, but this can also lead them to be a nuisance in some places (Credit: Loic Venance/AFP/Getty Images)
Whether North American gulls will become more urbanised like their cousins in Europe, remains to be seen, but there are some signs they might.
In Victoria, the capital of British Columbia, Canada, seabird ecologist Louise Blight has surveyed the nests of glaucous-winged gulls using drones. Downtown numbers have increased ten-fold since the 1980s. Some have also moved their nests further from the shoreline – though just a kilometre or so. It may allow them avoid predators such as bald eagles, says Blight.
Chemical analysis of glaucous-winged gull feathers collected between 1860 and 2009 points to the birds consuming less fish over time, which Blight links to a fall in availability of fish. This might have pushed these generalists to seek sustenance elsewhere. But Blight believes this is not tied in with urban nesting. "We see rooftop nesters feeding their chicks with fish also," she explains.
"We tend to think of gulls as just garbage eaters, but there's a lot of research showing that they do best when eating fish," she says.
The gulls initially moved into our cities and suburbs, say gull biologists, due to the safety high roofs offer from disturbance and predators. But ecologically gulls are jack-of-all-trades and opportunists. One study of lesser black-backs transferred gulls between a Russian island and southern Finland discovered that the birds were not locally adapted, but rather just very flexible at exploiting whatever habitat they find themselves in.
"Gulls are at the high end of avian intelligence," says Rock. Their natural curiosity and ability to learn helps them adapt to new environments. A recent study found that more than half of gulls were willing to touch and explore a plexiglass food box on a beach.
But the movement of gulls into urban areas brings some well publicised problems – the birds' typical tactic for defending their nests is to circle intruders or divebomb anything that ventures too close. Unfortunately, in towns and cities, that invariably means humans. Most direct attacks don't involve any contact, but aggressive gulls may strike with their feet. The noise produced by large colonies of these birds also attracts a lot of complaints from human residents, says Rock.
In many countries around the world, gulls are moving further inland as urban areas offer them new habitats (Credit: Paul J. Richards/AFP/Getty Images)
But controlling the numbers of these new urban birds is not straightforward. Some UK local authorities put oil on the bird's eggs to stop them hatching, or try to disturb them with loud noises or hawks, or even poison them.
Many experts urge, however, that we instead learn to live with these new neighbours. Herring gulls and black-backed gulls, the two urbanites in the UK, have seen their overall numbers decline by 60% and 30% in the last 25 years.
In Canada, Blight says people harbour a love-hate attitude to gulls. "They are intrinsically beautiful birds and people have a grudging respect for them," she says. "Urban gulls bring nature into the city in a world that is increasingly less exposed to nature."
And as the cries of gulls now become part of many urban soundscapes, perhaps we should simply marvel at ingenuity that has allowed these sea birds adopt our home as their own.
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