An afternoon stroll through Barcelona with a sandwich in hand has become a high-risk activity, as the city’s increasingly audacious gull population has earned a new nickname: the “pickpockets” of lunchtime snacks.

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These birds have developed a remarkable, if unwelcome, skill for snatching food directly from the hands of unsuspecting people. The phenomenon is particularly pronounced in the bustling Plaça de la Gardunya, adjacent to the world-famous La Boqueria market. Here, gulls watch from the market rooftops, patiently waiting for the right moment to swoop down on anyone distracted by their meal.

According to research reported by betevé, this is not random behaviour but a calculated strategy. The gulls, predominantly the native Yellow-legged Gull (Larus michahellis), have learned to identify hotspots for accessible food, and the rise of takeaway services from market stalls has created a perfect hunting ground.

Joan Navarro, a researcher at Barcelona’s Institute of Marine Sciences (ICM-CSIC), explains that the birds have become expert profilers of human behaviour. “They have learned to steal food from us,” he said. “These birds know that many people won’t confront them and will drop the food on the ground. They take advantage of it like a good pickpocket.”

“We have identified individuals and locations in Barcelona where the gulls know they will find food with minimal effort,” Navarro added, noting that the area around La Boqueria is a prime example due to the prevalence of people eating on the go.

From Seafarers to City Dwellers

The Yellow-legged Gull, a species typically found along the Mediterranean and Atlantic coasts in communities like the Medes Islands and the Ebro Delta, first began establishing itself in Barcelona around the 1970s. Initially, their presence was confined mainly to the port, where they fed on scraps from fishing fleets.

However, over the past decade, the gulls have undergone a significant behavioural shift. They have adapted to new urban food sources, including waste from the high concentration of restaurants along the coastline and, most effectively, food from tourists and locals in busy public spaces.

Today, an estimated 350 breeding pairs of gulls reside in Barcelona. They nest in elevated locations, such as the cliffs of Montjuïc and the city’s many rooftops, from mid-March until July. Each pair typically raises one or two chicks annually, and the young have a strong tendency to remain and breed in their birth area. GPS monitoring by the ICM-CSIC confirms this, showing most gulls operate within a 50-kilometre radius of their nesting site.

While their food-snatching antics are a growing nuisance, and a far cry from more serious crimes like the recent theft of 71 phones, these birds are now the focus of a major scientific study.

Winged Sentinels for Public Health

Since late last year, Navarro and his team at the ICM-CSIC have been running a project called ‘Aliats’ (Allies), which aims to use the urban gull population as a bio-indicator for the city’s environmental health.

“We want them to be our sentinels,” Navarro explained. The research involves capturing some of the urban gulls and taking biological samples. By analysing these samples, scientists can determine the presence and origin of various pathogens and contaminants in the urban environment.

The findings from the ‘Aliats’ project could prove vital. The ultimate goal is to apply these results to shape and inform public health policies in Barcelona. In an ironic twist, the same birds that have become infamous for pickpocketing sandwiches may soon provide invaluable data to help protect the very citizens from whom they steal lunch.