The world's most threatened gull calls New Zealand home, but most Kiwis don't know it

Monday, 8 January 2018

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

New Zealand has more than 900 native species approaching extinction and another 2800 declining or at risk – yet Kiwis believe we are doing a good job on conservation. In this Forgotten Species series, GED CANN asks are we simply believing our own advertising, and forgetting about those species that aren't given airtime?

Anyone who has ever enjoyed fish and chips at the seaside wouldn't believe there was a threatened gull in New Zealand.

However, the native black-billed gull – the most threatened gull on the planet – is in serious decline.

The black-billed gull prefers to nest near coastlines.

The Department of Conservation (DOC) classifies the black-billed gull as nationally critical, with a population of about 60,000 breeding adults, which is expected to decline by up to 70 per cent over 10 years or three generations, whichever is the longest.

* Native birds in 'desperate situation' with 80 per cent threatened**

That puts it in the same category as the black robin, but unlike the robin, the black-billed gull looks very similar to a species most of us consider a pest – the red-billed gull.

It may look like many other gulls, but the black-billed gull is a rarity.

Appearance is where the similarity ends because, unlike other gulls, this species favours nests among the shingle of braided riverbeds to the coastline, and is smaller, more timid, and far less likely to pinch a chip.

Edith Smith is involved with BRaid, a group advocating for saving New Zealand's braided rivers, and said the black-billed gull was facing mounting pressures from predation and a growing risk of sudden floods wiping away its nests.

The new year brought a reminder of just how vulnerable these birds are, with heavy rains all but wiping out a colony of 3000 gulls nesting near the State Highway 1 bridge over the Hakatere River near Ashburton, in Canterbury.

Smith said up to 2500 chicks drowned in the floods.

'The remaining adults appear to be quite unsettled, with many preening or tucking heads under their wings. Only one or two older chicks possibly from the earlier colony remain. The colony has been washed clean with no sign of the nesting materials or guano of a few days ago.

A black-billed gull colony near the State Highway 1 bridge over the Hakatere River, in Canterbury, had hundreds of chicks before heavy rains early in the new year.

'Some clusters of gulls have moved further downstream and can be seen in the distance. While most of the younger chicks were too immature to float down the river to higher ground, some may well have survived.'

A second, larger, colony at the river mouth nested earlier than the SH1 group, meaning their young would have been mature enough to fly or move to higher land.

Almost no chicks remained after the rains.

Smith said the birds preferred braided rivers for their invertebrate prey, but pollution from intensive farming meant even this food source could prove unreliable.

Braided rivers were also more likely to remain polluted for extended periods, because they don't get the cleansing floods common in alpine rivers.

The gulls formed colonies, and childless gulls often babysat nestlings while their parents were foraging, keeping them safe from predators.

'If something like a ferret or a stoat … comes ferreting around, they fly up and so that sudden noise and flapping of wings will often scare the predator away.'

Smith said a study of black-billed gulls in Southland had found if the population continued to decline at the same rate there could be a crisis point reached within the next generation.

Black-bills routinely migrate to the warmer North Island or upper South Island, and return to the braided rivers around August as they scout for nesting spots.

There is hope as the gull's profile grows, reflected in the number of votes it received in Forest & Bird's Bird of the Year competition, climbing from 72 to 900 in 2017.

'Somebody likes them,' Smith said.