Our Changing World: Burrowing into the mystery of Great Barrier Island's black petrels

RNZ News

14-05-2025

An adult black petrel cruises over the waters of the Hauraki Gulf.
Photo:
Dan Burgin / WMIL
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Tracking what one of New Zealand's most vulnerable seabird species gets up to on the other side of the Pacific may help answer the question of why so many fledglings never return, a veteran researcher says.
Juvenile black petrels (tāiko/tākoketai) hatched on Great Barrier Island - one of two remaining colonies - have just fledged from their burrows to undertake their maiden migration to the Galapagos Islands and the coast of Ecuador.
Wildlife Management International managing director Biz Bell says this breeding season appeared to have gone smoothly, with most petrel parents managing to successfully raise their single chick.
"A lot of really good condition chicks this year, which is really pleasing, lots of really fat chicks," Biz says.
"Our breeding success is about 72 percent, on average, and it looks like this year is going to be an on-average year, which is really exciting."
Tākoketai are classified as nationally vulnerable, and their already small numbers are
gradually declining
.
There are about 15,000 black petrels left in the world, and all of them nest on either Aotea Great Barrier Island or neighbouring Hauturu-o-Toi Little Barrier Island, in burrows they dig into the ground.
Bell and her team have been surveying the petrels for 29 years.
The survey, which is funded fifty-fifty by the Department of Conservation and a fisheries levy, includes three fortnight-long trips to the colony every year, with the aim of checking every one of the nearly 500 study burrows at least once each visit.
Wildlife Management International managing director Biz Bell.
Photo:
RNZ / Kate Newton
Since the survey began in the mid-1990s, about 5500 chicks have been banded but fewer than 500 have ever been found again.
"Is that because we can't search this entire, massive island and they're somewhere else?" Biz says.
Predation on land is largely under control, so the main threats to petrels are at sea, she says.
"Are they dying on migration? Are they dying in fishing boats? Are they dying from pollution events, climate change? It's one of our biggest gaps of knowledge."
The petrels are at particular risk from getting hooked by long-line vessels, because of their scavenging habits and diving proficiency.
Biz says the team knows a lot about the petrels' habits on this side of the Pacific but she hopes that next season, they might be able to start a closer collaboration with researchers in Ecuador.
Ecuadorian ecologist Giovanny Suarez Espin was due to join the survey's final trip to the colony in April but was unable to get a visa in time.
He will now join the Aotea survey for the 2025-26 season instead, Biz says.
"He's a research scientist, he does a lot of work at sea there and he's monitoring black petrels there because it's also a special species for them."
WWF-New Zealand chief executive Kayla Kingdon-Bebb, left, and board member Kerry Prendergast check a black petrel chick.
Photo:
RNZ / Kate Newton
Biz hopes the New Zealand team will also be able to travel to Ecuador in upcoming seasons to build a better picture of what is happening to the juvenile birds.
Those young birds typically stay in South American waters, feeding off the Humboldt current, for several years before they return to the Great Barrier colony for the first time.
"It's a long time in their waters [and] they're interacting with fishers all the time," Biz says.
"Is there a specific risk that our chicks, in particular, are dealing with over in Ecuador?
"What we'd really like to do is go over to Ecuador, get out on some of these vessels, catch some birds at sea, put some loggers on and get some tracks of how they behave in those waters, where they go ... and see what happens."
Since last year, long-line fishers in New Zealand waters have had to use all three internationall-recommended practices to prevent seabird by-catch.
That includes using weighted hooks to ensure the hooks sink quickly, installing tori lines (bird-scaring streamers) above boats, and only fishing at night, when birds are less likely to be feeding.
However, those practices do not necessarily not extend to the rest of the birds' habitat, Biz says.
"We're basically building relationships with researchers and fishermen over in Ecuador through both high-level government relationships but also personal relationships with fishers and with scientists to try to get that sort of mitigation happening over there as well."
In Depth reporter Kate Newton visited Aotea-Great Barrier Island this summer to see how the survey team goes about its work.
Photo:
RNZ / Kate Newton
The main survey on Aotea will keep going for as long as possible, she says.
"Longevity studies are super-important and we find something new every year. We don't know enough about these birds yet even though we've studied them for nearly 30 years."
The petrels are "absolutely magic".
"I will come back as long as I possibly can."
Listen to the episode to learn more about how Biz and her team go about monitoring the petrels, the threats the seabirds face, and what the survey has uncovered over nearly 30 years of research.
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WWF-NZ paid for Kate Newton's flight to Great Barrier Island. The organisation had no oversight of this story or podcast.