Hundreds of dead red-billed gulls at Taiaroa Head on the Otago Peninsula are no cause for concern, the Department of Conservation says.
As many as 20 or 30 juveniles were being found dead around the Taiaroa Head car park each day, upsetting some visitors.
But it was normal for weak chicks to die at this time of year and DoC staff were not worried, Coastal Otago conservation services manager David Agnew said.
"We've had queries about the dead gulls, but we don't think it's anything unusual," he said.
As colonial birds, the gulls nested in close proximity and breeding pairs commonly had two or three chicks, not all of which were expected to survive.
Chicks were also more susceptible to diseases easily spread within the colony, Mr Agnew said.
He and other DoC staff monitored the gulls and had found no evidence of large numbers dying from diseases.
"There's nothing that's raised our concerns, and if there was, we've got a protocol for sending birds up to Massey for analysis. But from what we've seen so far, it's the usual deaths that happen every year," Mr Agnew said.
Otago Peninsula Trust Taiaroa Head operations manager Hoani Langsbury said it was a classic case of "survival of the fittest".
Up to 30 birds would be found dead every day for four or five weeks, until about February, he said.
"We're talking about 15 percent, or something like that at a guess, don't survive. There are about 800 nesting pairs above the [albatross] centre and about 2000 in the wider area, and they can each have two or three chicks," he said.
Mr Langsbury and others monitored Taiaroa Head for predation and had ruled that out as a cause of death among the gulls.
They had also found plenty of food in the area, he said.
Mr Langsbury said the birds being found dead were all chicks, which had started to fledge around Christmas.
If adult birds were dying, that would be a worry, he said.
"When they fledge, there is a percentage that never make it. Either they don't have enough resource on their bodies when the parents kick them out of the nest, or they haven't learned to fend for themselves."
"Some visitors get upset but it's a natural process."
He collected dead birds regularly so they would not attract predators.
Natures Wonders owner Perry Reid, whose property adjoined the Taiaroa Head car park area, had a different theory.
He said red-billed gull chicks were being run over by vehicles, which he had witnessed.
Mr Reid's theory was one which had not been considered by DoC staff or Mr Langsbury.
A Forest and Bird spokesman said red-billed gulls were native to New Zealand and fully protected under the Wildlife Act, but were not considered threatened as the almost identical black-billed gulls were.