At this stage in the gulls' breeding season, up to 1000 chicks congregated in the car park in the evenings, and it was only a matter of luck that more birds were not killed, Langsbury said.
The gull colony at Taiaroa Head had grown significantly over the past 10 years — increasing by 1000 pairs — and was the only red-billed gull colony in New Zealand that was not declining.
Whether the drivers were intentionally targeting the protected species or not, the entire headland was a seabird colony, he said.
Years of conservation work supported not only Dunedin's northern royal albatross and the red-billed gulls but more than 20 species of seabirds, he said.
Department of Conservation ranger Colin Facer called driving over and killing adult birds and chicks "abhorrent".
Red-billed gulls were more threatened than the northern royal albatrosses that bred on the peninsula, he said.
The chicks of killed adults would not be fed, leading to further deaths, Facer said.
The species also acted as sentinels for other species in the area such as the royal spoonbill.
In the past, other species on the peninsula including penguins had been intentionally targeted by drivers.
Those responsible could be prosecuted under the Wildlife Act, he said.
