Black-billed gulls return to Christchurch for nesting season

The most threatened gull on earth has returned to an unexpected site for a second nesting season. 

The black-billed gulls are only found in New Zealand, and the critically-endangered species have made the most of an earthquake-ruined city.

While their Christchurch home doesn't look like the most attractive, it's their own slice of paradise, complete with maternity suite.

"It's got the fence around which gives them a bit of privacy, and the water pooling around it gives them some protection as well," says Department of Conservation biodiversity ranger Anita Spencer.

This season, around 30 of the rare seagulls have returned to the half-demolished and flooded foundations of the former office block in central Christchurch, but that's significantly fewer than last year's 300. 

However, joining them are around 70 red-billed gull friends.

"I wonder if there's some dynamic between the two species that means the red-billed species has got the advantage here," Spencer says.

Despite it being extremely rare for gulls to set up a colony in the city, they are breeding and nesting with over 100 nests spotted on-site.

The Catholic cathedral precinct has plans to build a car park and offices on the land, but they're not overly thrilled with the avian visitors. 

"They've arrived, nature will have its way... we'll just have to tolerate them," says head of Christchurch Catholic diocese's property team Tony Sewell.

That's because these nesting birds can't be disturbed. Black-billed gulls are only found in New Zealand and are the most threatened gull species in the world. 

Populations have rapidly declined by 80 percent, putting them in the critically-endangered category.

"They are endangered birds and they're protected under the Wildlife Act," says Spencer.

The Cathedral precinct is now pumping the water out of the area and has plans to put nets in next year to stop the gulls from getting in.

"They are migratory, so they'll find somewhere else to go," says Sewell.

The Department of Conservation is hoping the decline of black-billed gulls at the derelict site means they've worked out their natural home at the South Island's braided rivers is a far more pleasant one.