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Nest cams on the Ashley River bed captured four wheel drive vehicles and motorbikes driving through the colony last week, with the Canterbury Regional Council reporting that 10 birds were killed.
The native birds are protected and classed as a critically endangered species.
DOC North Canterbury operations manager Kingsley Timpson said rangers are making good progress to find those responsible.
Disturbing black-billed gulls could result in a $100,000 fine and/or two years in jail.
It was currently the middle of nesting season for the birds, which are the most threatened gull species in the world, Timpson said.
The area is regularly monitored by the Ashley-Rakahuri Rivercare Group and the Canterbury Regional Council.