The Dunedin City Council’s plan to lower the number of the native birds in the city from 10,000 to about 5000 over the next five years relies on dispersal techniques and interrupting breeding of the abundant birds.
The council plans to cover freshly laid eggs in oil to stop them from hatching at two major urban nesting sites and encourage Te Rūnaka o Ōtākou to harvest eggs at sites yet to be determined in order to avoid poisoning the native species, which could pose problems for Dunedin Airport after the Green Island landfill stops accepting food waste.
SPCA science officer Dr Alison Vaughan said when human activities had the potential to negatively impact the welfare of wild animals, there was a duty to ensure the activities were done in a manner that minimised the injury, pain, or distress to animals.
"We are glad to see the council conducting a robust assessment and planning ongoing monitoring of their management plan to help ensure the goals are met.
"We also support the council taking steps to enable the use of more humane, non-lethal methods of population control, such as dispersal and egg removal.
"We encourage the council to avoid the use of less humane methods of pest management, such as use of poisons to kill birds," Dr Vaughan said.
The council’s draft southern black-backed gull management plan, part of its application to continue operations at the Green Island landfill, said poisoning the birds with alpha-chloralose baits at nesting sites would not be considered this year while alternative methods were used.
It could be considered next year, but culling the birds was not expected to be necessary, the plan said.
Creating a black-backed gull management plan to manage food availability at Green Island was a condition of consent for the planned Smooth Hill landfill after fears were raised the risk of bird strike could increase with a new landfill close to the airport and the closure of Green Island, known habitat for thousands of gulls.
By January 2028, Dunedin’s estimated population of 10,000 black-backed gulls would be halved, the plan said.
Fewer than 100 birds would be frequenting the Green Island landfill.
More than 500 eggs would be oiled or harvested.
Oiling eggs shortly after they were produced would stop a "gaseous exchange" through the eggshell, preventing chicks from hatching.
Walton Park sand quarry, in Fairfield, where oiling would occur, had 62 nests, the plan said.
Logan Point Quarry, in Logan Park, the other site where oiling would occur, had 30 nests.
The new Dunedin hospital construction site, in the city centre, was the other main breeding site in the city, the plan said.
It had 10 nests.
It was also suspected gulls were breeding at the mouth of the Leith, where 60 gulls were seen.
Lake Waitahuna River, about 40km west-southwest, is a major breeding site with 400 breeding gulls, but along with those at Lee Stream and Lake Mahinerangi, it was assumed those birds did not interact with coastal birds and did not rely on the landfill as a food source.
The plan also said that colour-marking would be used to monitor the birds as they were dispersed from the Green Island landfill.
Staff would turn sprinklers on and mist the birds for a couple of hours each day to get them accustomed to being covered in water droplets.
Then, a small amount of coloured dye would be added to the solution to colour-mark the birds and assist with monitoring them.
GPS trackers would also be used on 10 birds, for more detailed data.
From this month through August a team of trained wildlife staff would use a range of tools — from a gas cannon, starter pistol and pyrotechnics to kites, balloons and arm-waving — to disperse the birds from the area, the plan said.
After rapid population growth after European arrival in New Zealand, the native birds were "widespread and super-abundant" and therefore not protected.
