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Dunedin City Council education and promotions officer Catherine Gledhill said, although gulls rummaging through rubbish was not considered a significant issue, it was a "nuisance" when it did happen.
Food scraps inside the black bags were the main cause, particularly when left on the street for extended periods of time.
It meant the city’s centre was the main target for the gulls, as there were more food outlets around, Ms Gledhill said.
"The collection of city council rubbish bags is carried out each night in the CBD areas, beginning at 6pm.
"People are asked not to put their bags out for collection before 5pm, and to retrieve their bags from the kerb if they miss the collection truck that evening."