Seagulls from a species that feeds on human rubbish are harbouring highly drug-resistant superbugs, a study found.
Researchers analysed 57 samples of droppings from the yellow-legged gull Larus Cachinnans.
They found that one in 10 carried superbug bacteria resistant to the "last resort" antibiotic vancomycin, which is used when most others have failed.
The white and grey birds, recognisable by their bright yellow legs, can often be seen flocking on rubbish tips.
Scientists collected the samples off the Portuguese coast.
Lead researcher Dr Gilberto Igrejas said: "We used a novel technique called proteomics to detect the maximum number of bacterial proteins which are thought to be connected in some, as yet unknown, way to antibiotic resistance."
It is thought migrating gulls might be one explanation for how antibiotic resistance is spread from place to place.
The scientists identified several strains of enterococcus bacteria in the seagull samples.
The bug often lives harmlessly in the human gut but can cause serious infections in vulnerable people.