Tourists have been disturbing populations of one of New Zealand's most threatened bird species at a Rotorua geothermal attraction - a few months ahead of the critical breeding time for the species.

According to the Department of Conservation, rangers have received multiple reports of groups of tourists disturbing black-billed gulls around Sulphur Bay causing them to take flight towards nearby commercial operations.

Rotorua is home to three different gull species, two of which are classed as threatened. Black-billed gulls are classed as being 'nationally critical' - one step away from extinction and more threatened than kiwi.

Although relatively common in Rotorua, the worldwide population of black-billed gulls has been steadily declining at a rapid rate leading to the species being tagged as the world's most threatened gull species.

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Both the water and the rocky shore around Sulphur Bay have Wildlife Refuge Status or Wildlife Sanctuary status - the highest order of protection in New Zealand.

Both the water and the rocky shore around Sulphur Bay have Wildlife Refuge Status or Wildlife Sanctuary status. Photo/File
Both the water and the rocky shore around Sulphur Bay have Wildlife Refuge Status or Wildlife Sanctuary status. Photo/File

Department of Conservation ranger supervisor Caraline Abbott said they had previously erected warning signs in the area to let visitors know entry into the sanctuary was unauthorised.

"We've also added an interpretation panel which raises awareness of the threatened bird species.

"Although there may be thousands of black-billed gulls in Sulphur Bay, the recent fledgling rate from this population has been low and this is likely partially due to disturbance from humans. "

Ms Abbott said the department had been monitoring this population for years because of its threat status and it was unfortunate people did not recognise disturbing this bird was an issue - particularly if they were nesting.

Rotorua Lakes Council administers a walkway around the bay and into the Sanatorium Reserve however visitors had been known to cross barriers and wander into unauthorised areas.

"Visitors crossing walkway barriers are not only compromising their own safety by being in geothermal areas, but are contradicting legislation established to protect our native species," Ms Abbott said.

While the gulls are commonly found at the lakefront, where they regularly encounter human disturbance, they are unlikely to nest in this area and are more likely to nest in the quieter parts of the bay.

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Black-billed gull nests are camouflaged against the geothermal landscape making them susceptible to being trampled by foot traffic.