Seagulls endangered in New Zealand

Seagull is NZ's latest endangered species

Seagull numbers in New Zealand are falling so quickly the birds now appear on threatened species lists, alongside the kiwi and the kakapo.

Stuff,

30 October, 2014

A Department of Conservation report on bird numbers has classified the black-billed gull "nationally critical", the most serious category, usually reserved for our rarest birds, because of the rate of expected decline.

Numbers were predicted to drop by more than 70 per cent over the next 30 years.

There were an estimated 180,000 to 200,000 of the birds in 1977. There are now thought to be 60,000 to 70,000.

The red-billed gull, the mainstay of Kiwi beaches, is "nationally vulnerable".

Numbers have been falling sharply at the three main breeding colonies and are expected to drop by between 50 and 70 per cent over the next three decades.

The current population is thought to be fewer than 100,000.

The black-billed gull is found almost entirely in the South Island, mostly in Southland, living inland and nesting on braided rivers.

"Their numbers have crashed for some unknown reason," DOC bird scientist Hugh Robertson said.

Predators such as wild cats, stoats and ferrets were thought to be partly to blame.

Global warming could also be at play, Robertson said. It influenced changes in currents at sea, which affected food supply, and the water flow in rivers.

"The lower the flow, the islands [in braided rivers] are less defendable. It makes them more accessible to predators.

"You've [also] got weeds growing on the gravel so there's more cover for predators. They can get closer before they're detected."

Humans destroying habitat, through activities such as four-wheel driving, was a problem too, he said.

"I think people just see small gulls and think "just bloody seagulls" without realising they're part of native birdlife and have a right to be there."

Ornithological Society of New Zealand marine bird expert Graeme Taylor said gulls played an important ecological role in New Zealand, sustaining reptiles, invertebrates and rare plants such as Cook's scurvy grass.

"They may not be quite as popular as the kakapo because people think of them pooping on them and stealing their bread, but how many kids wouldn't get fun out of feeding seagulls down by the beach? If they were to disappear it would be quite a loss to the New Zealand coastal scene."

Taylor is leading a major count of red-billed gulls over the next year. Populations may have been falling even before the only other national headcount, in the 1960s, he said.

"Because it's a species that's quite long-lived it can take 100 years before you see a significant change in the numbers. As long as the adults aren't being killed, it will be a long, slow decline."

Seagulls can live up to 30 years. About 1500 red-billed gulls bred in nine small colonies on Banks Peninsula, Christchurch City Council ornithologist Andrew Crossland said, but thousands more flocked to the city to feed in places like the Avon-Heathcote estuary. Many came from the large breeding colony at Kaikoura.

"Christchurch is a major post-breeding wintering site for birds like the red-billed gull," he said.

"These birds rely on [the habitats of Christchurch] for half of their annual cycle."

He and his team would be measuring the local population for the national count and assessing the threat of predators.

Black-billed gulls used to be common in Canterbury, he said, nesting in many braided rivers like the Waimakariri, Rakaia and Ashley, but breeding was now limited largely to the Waimakariri.

"It's like the bottom's fallen out of the population."

BY THE NUMBERS

Black-billed gull: 1977: 180,000 - 200,000 birds. Now: 60,000 - 70,000.

Red-billed gull: Now: Fewer than 100,000 birds. Expected to fall by 50 to 70 per cent in the next 30 years.

FACTS 

• Seagulls live for about 30 years.
• Black-billed gulls used to be more common than red-billed in New Zealand.
• A young black-billed gull has a reddish beak. A young red-billed gull has a black beak.
• There are three major breeding colonies for red-billed gulls: Kaikoura, the Mokohinau Islands in the Hauraki Gulf and the Three Kings Islands north of Cape Reinga.
• Black-billed gulls are endemic to New Zealand.