Black-backed gulls targeted to protect rare bird species on Canterbury's braided rivers

Monday, 26 August 2019

DOC classifies the black-billed gull as nationally critical - but few people appreciate how rare it is (first published January, 2018)

More 80 per cent of southern black-backed gulls/karoro will be eradicated in two Canterbury rivers bid to save their rare and threatened cousins.

The gulls prey on the chicks and eggs the endangered black-fronted tern/tarapirohe, black-billed gull/tarāpuka, wrybill/ngutu pare, and banded dotterel/tūturiwhatu.

The Department of Conservation (DOC) aims to reduce the population of black-backed gulls in the Waiau and Hurunui rivers by more than 80 per cent over the next five years.

Black-fronted tern chicks are vulnerable to predators.

DOC science advisor Kerry Weston said a successful trial control operation was carried out on the Hurunui River last year.

**READ MORE:

Trail camera footage shows a black-backed gull preying on a chick.

* Black-billed gulls relocate after devastating floods

* Large colony of endangered gulls nesting on Canterbury's Ashley River

The Department of Conservation aims to protect black-fronted terns and other braided birds with a gull control programme in North Canterbury.

* Ashley Rakahuri Rivercare Group's efforts recognised across the Tasman**

It will be the first time black-backed gulls have been controlled in the Waiau River, where they have established several large breeding colonies.

'Last year the control operation was really successful, we managed to reduce 90 per cent of gulls in some locations. Unfortunately, due to severe flooding many of the birds we were trying to protect ended up abandoning their nests but we expect more of them to nest successfully in the future,' Weston said.

To measure the success of the control operations, DOC will compare the breeding success of the threatened bird species in areas where gulls are controlled with areas where they are not.

DOC is overseeing the control programme, with the support of Environment Canterbury as part of the Hurunui Waiau Water Zone Committee's flagship project to restore riverbed habitat and support threatened bird species.

Zone committee deputy chairman Ken Hughey said Canterbury's braided rivers were unique and supported important fish, animals and plants.

'Many of the special bird species that depend on these rivers are declining,' he said.

Ecological consultancy Wildlife Management International will carry out the control work by targeting black-backed gull colonies over a 30km section of the riverbed between the upper and lower Hurunui gorges for several weeks.

They will also be working over a 70km section of the Waiau riverbed. Control will begin in the next few weeks and may continue until the end of December. Landowners living next to the areas where gulls will be controlled have been informed and will be contacted again before operations start.

The toxin alpha-chloralose, an anaesthetic compound registered for black-backed gull control, will be mixed with margarine on bread bait and hand laid within gull colonies. Uneaten baits and gull carcasses will be removed within 24 hours. Warning signs will be in place at entry points to the operational areas.

Alpha-chloralose bread baits and gull carcasses are toxic to domestic animals, as well as people, if eaten. People are advised to avoid the control areas while signs remain in place and not to take their pets into these areas.

Southern black-backed gull/karoro is abundant throughout New Zealand and has reached unnaturally high densities in some areas due to food supply from human sources. This species is also common at similar latitudes in southern Australia, South America, southern Africa and the subantarctic islands.