The draft southern black-backed gull management plan is included in the Dunedin City Council’s application to extend the resource consents for the city’s Green Island landfill for up to seven years, before a new landfill at Smooth Hill is opened in 2028-29.
Creating a black-backed gull management plan was a condition of consent for the Smooth Hill landfill after fears were raised by Dunedin Airport and others the risk of bird strike could increase with a new landfill close to the airport and the closure of Green Island landfill, known habitat for thousands of gulls.
By January 2028, the plan said the estimated population of 10,000 native, but unprotected, birds would be halved.
There would be fewer than 100 birds frequenting Green Island landfill.
And more than 500 eggs would be oiled, so as not to hatch, or harvested by Te Rūnanga o Ōtākou from breeding sites.
Monitoring for the plan would increase next month as a "dispersal" from Green Island landfill was planned, the draft management plan said.
"It is not anticipated that culling will be required," it said.
"If the initial dispersal in 2023 results in unacceptable offsite impacts, it may be necessary to consider a culling programme in 2024 in the lead-up to the change in landfilling practices.
"This would include alpha-chloralose baits at nesting sites.
"Detailed protocols would be established only if culling is deemed to be necessary."
To understand the birds’ behaviour, colour-marking would be used to monitor the birds as they left 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.
In June, July and August this year, and then April, May and June next year, 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.
Broadly, closing Green Island and opening Smooth Hill, where food waste would not be accepted, was likely to reduce the number of gulls in the area over time.
In the near term, the council expected to introduce a new kerbside collection of waste that included a separate bin for organics, or food waste.
When the change took place, food waste would no longer be a part of the general waste stream heading into the landfill.
Food waste would instead be taken to a new organics processing facility due to be built at Green Island in 2023-24, the draft plan said.
Food-free bulk waste would then be accepted at Green Island until Smooth Hill became operational, targeted for 2028-29.
In the short to medium term the black-backed gulls would begin searching for food elsewhere as waste management practices changed.
During that time if the birds relocated to Sinclair Wetlands, Lake Waipori, Lake Waihola, or farmland near the airport, they could more regularly pass through airplane flight paths and increase the risk of bird strike at the airport.
City amenity could also suffer if birds increasingly defecated in the city centre, bothered people for food, or otherwise created a mess.
Black-backed gulls might also spread disease, or prey on lambs or old sick sheep, the plan said.
Gull numbers appeared to be highly variable over the course of a year, and at Green Island landfill the maximum count of 8320 gulls recorded in July last year compared with a low count of only 2240 a month earlier.
An aerial survey in November recorded 9216 gulls in the Dunedin area.
During that count there were 3112 black-backed gulls at the landfill, and 6104 offsite, the plan said.
