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Trouble or treasure . . . About 20 people attended a Waitaki District Libraries-organised public talk at the Scottish Hall on Tuesday night about Oamaru's red-billed gull problem. PHOTOS: REBECCA RYAN/HAMISH MACLEAN

Over the past seven years, the number of red-billed gull nests in Oamaru has increased by 500%.

But elsewhere in the country, it is a very different story.

Nationally, the population of red-billed gulls/tarapunga has declined by about 30% over 50 years — it is one of only two bird species in New Zealand whose population decline can be attributed purely to climate change — and as a result their status had been updated to at risk/declining, protecting them under the Wildlife Act.

At a public talk at the Scottish Hall in Oamaru on Tuesday night, researcher Dr Chris Lalas and New Zealand Marine Studies Centre director Sally Carson busted some of the common myths about the gulls, including why they have taken up residence in Oamaru’s central business district, and called on the public to get involved in the Great Otago Gull Count next month.

In 2014, there were about 3000 red-billed gull nests in Otago, from the Waitaki River mouth in the north to Nugget Point in the south. Last year, there were 8000, including 500 in Oamaru and 150 in Kakanui.

While the gulls had consistently nested at the Waitaki River mouth over the years, the first year in recent decades that they started nesting in Oamaru was 2015, when 150 were counted at Normanby Wharf. Since then, they have taken up residence at the Oamaru breakwater and moved into the central business district, creating an unwanted disturbance for many business and building owners in recent years.

Many people believed the move into town was connected with the closure of the Oamaru landfill in 2017, but Dr Lalas said while the timing was ‘‘pretty well spot on’’, it was a coincidence, not a cause. There was no question the gulls fed at the landfill in the past, but ‘‘there’s no record of red›billed gulls nesting in the old landfill — so they couldn’t have been displaced’’.

Research had revealed nesting on buildings was not related to the proximity of food. Gulls recognised buildings as safe sites, Dr Lalas said.

‘‘Each building is the equivalent of a predator›free island.’’

Dr Lalas said it was ‘‘unacceptable’’ in the long term to have the birds nesting in such close proximity to people.

‘‘There are hygiene issues and very definitely smell issues’’.

Business and building owners had tried several deterrents, including spikes, wires, flag lines, lasers and kites, to carefully encourage the protected birds to nest elsewhere.

Some people believed extermination was the answer, and it was something that had to be considered if non-lethal methods did not work, but it was important to remember the gulls were not ‘‘deliberately doing the wrong thing’’, he said.

‘‘We’re not out to punish the gulls, we’re out to stop them nesting in places we don’t want them nesting.’’

Researchers across the world were yet to come up with a permanent solution to red› billed gull problems in coastal towns, and Oamaru could be ‘‘leading the way’’, Dr Lalas said.

An ‘‘extremely effective’’ motion-sensor sprinkler system had been designed by Waitaki District Council staff, and after it was installed on one Oamaru building’s rooftop, nest numbers dropped from 50 to zero.

The council and Department of Conservation were also trying to lure the gulls to a decoy site at Cape Wanbrow. While it had not been very effective so far, it was too early to give up on it, Dr Lalas said.

During Sea Week, from March 7-11, all schools across Otago are being encouraged to take part in the Great Otago Gull Count, and count the number of gulls in their schoolyard over the course of one day.

Ms Carson said the Royal Albatross Centre-led project was designed to understand where different species of gulls were spending time and why, with the aim of reducing negative interaction between humans and gulls.

She also encouraged members of the public to report where red›billed gulls were nesting in Oamaru, so researchers could get a better estimate of population trends. Nest sightings can be reported online at inaturalist.org/projects/red-billed-gull-nests-in-otago.