The "Green Island Resource Recovery Park Precinct Bird Hazard Report" said with organic material no longer entering the landfill, in the long term the changes to Dunedin’s waste system would put a stop to the landfill acting as a "primary food source" for the city’s roughly 10,000 southern black-backed gulls — and numbers of the "high-risk species" would eventually dramatically drop.
However, in the short term, as the thousands of southern black-backed gulls that congregated there searched out a new food source, they could fly into the flight paths of aircraft, presenting an aviation hazard, the report said.
The changes at Green Island fit together with the city’s new waste collection system and plans for a new landfill at Smooth Hill.
Organic waste, including food scraps, is now processed indoors at Green Island and is no longer available for the birds at the landfill’s tip face.
As that change bedded in, thousands of birds were expected to abandon the site in search of food, a dispersal which had the potential to bring gulls into aircraft flight paths and present an aviation hazard, the report said.
The hazard assessment put the short-term increase to aviation safety at a "medium likelihood" without a management plan in place.
The assessment was based on monthly surveys at the landfill, around the region and at the airport, and it included a review of the airport’s bird strike data.
As long as no other food sources were provided, the risk of bird strike at the airport, 16km away, was expected to decline after the changes bedded in.
"In the short term [six to 12 months] however, the proposed changes would present a medium likelihood of SBBG [southern black-backed gulls] increasing the aviation hazard unless management actions were taken.
"This is based on: SBBG already being recorded in Dunedin Airport’s strike records; SBBG regularly being seen flying over the airport in relatively low numbers; and the large number of SBBG currently using the landfill as an important food source needing to find alternative sources," the report said.
"Because of their size and flocking nature and because of their presence in the strike records, SBBG are already a high-risk species for Dunedin Airport, therefore it is necessary to manage the potential risk associated with the moderate hazard rating."
In New Zealand, gulls, particularly the southern black-backed gull, presented "by far the most significant hazard to aviation.
"As scavengers, they exploit food sources at landfills, farms, parks, piggeries, fishing areas, and food-processing factories."
On one day last year 10,744 southern-black backed gulls were counted at the landfill.
The airport at present did not attract a lot of the birds, the report said.
The Dunedin City Council’s recently submitted application for the resource recovery park precinct at Green Island included a "draft southern black-backed gull management plan".
However, the Otago Regional Council said the application was specific to the resource recovery park precinct and was not for the wider Green Island landfill.
The regional council only had a draft management plan for the gulls, consents manager Alexandra King said.
Creating a gull management plan is a condition of consent for the planned Smooth Hill landfill.
Green Island is expected to operate until 2029-30, but the city council’s consent to operate it expired in October last year.
The Resource Management Act allows for consent holders to continue to exercise existing consents while applying for replacement ones and the city council applied to extend the consents for the landfill in May last year.
The application has been on hold since.
