The vanishing bird: The missing black petrels of Great Barrier Island

For nearly 30 years, researchers have been banding black petrel fledglings before they make their maiden migration to Ecuador. Only a handful of birds have ever come back.

Crouched on a steep slope in the forest, leaf litter sticking to my knees, my arm is stretched into a dark burrow and I am waiting for something to bite me.

Even with a glove on, the bite is sharp when it comes, and I have to fight the instinct to yank my arm back.

Instead, I wrap the rest of my fingers around the beak that still grasps my finger, and with some gentle pressure, walk the creature attached to it towards the burrow entrance, where I can pinion its wings and then hold it to my chest.

Someone else is already reading out the band number, so I concentrate on the bird: the sooty feathers shingled down its back, the webbed feet ending in delicate curved claws, the pale beak, a black eye staring back at me.

This is a black petrel, a tākoketai - a seagull-sized bird that only nests in New Zealand.

Once found across the North Island and near Nelson, the species has dwindled to a colony of about 5000 breeding pairs here on Aotea/Great Barrier Island, and a smaller colony on Hauturu/Little Barrier Island.

For nearly 30 years now, a team of conservationists have surveyed the Aotea colony, precariously located on the summit of Hirakimata/Mt Hobson, the island's tallest mountain.

The birds of the colony are good breeders. On average, more than 70 percent of petrel parents monitored by the survey successfully fledge a chick each year.

But of the thousands of chicks that have been banded over the decades, only about 10 percent of them have ever been found again.

What happens to the rest is still largely a mystery.

Biz and the birds

When Biz Bell was five, her dad Brian found a wandering albatross that had crash-landed at Lyall Bay in Wellington.

Injured and weary, it allowed itself to be bundled into the back of the family Kombi van, where it rode home to Seatoun alongside the stunned Bell children.

It was bigger than Biz, and beautiful. She couldn't stop staring at it.

Brian, a career conservationist, made the albatross comfortable in the garage, where it gulped down sardines and endured pats from the kids.

A week and a half later, on another bright, breezy Wellington day, they took it back to Lyall Bay and watched as it paddled out into the bay, launched itself into a run over the surface on webbed feet and, finally, caught the air and soared.

For Biz, that was that. "Seabirds have been it ever since."

That huge white albatross might have been the first seabird to change her life, but it's the much smaller black petrel that has defined it.

Biz was a 25-year-old ecology graduate when veteran ornithologist and New Zealand seabird guru Mike Imber asked her if she would lead a project to survey the tākoketai population - which had only been monitored opportunistically to that point.

"A question was being asked, about what's the impact of fisheries on our seabirds in New Zealand? And this was one of the key species because it had been caught as bycatch on several vessels."

For 29 seasons now, her family's company, Wildlife Management International, has led the survey, funded through the Department of Conservation and levies collected from the fishing industry.

No one was expecting the study to last as long as it has, and part of its value now lies in its longevity, she says.

"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."

She had done plenty of work with burrowing seabirds before the study began, but had never seen a black petrel.

"I just fell in love with them.

"They are bumbling, crazy little things on land but then you can go to sea and they're just mind-blowingly beautiful and majestic."

The hidden colony

During the New Zealand winter, tākoketai remain out over the Pacific Ocean, travelling as far east as the coastal waters of Ecuador.

But from October, the petrels begin arriving home, crashing through the canopy to land within metres of burrows they've previously clawed out of the soft dirt.

The birds nest all over Aotea, but the track to the main colony winds past bush-capped bluffs of volcanic rock, across an exposed, scrubby ridge, and up through dense, mossy forest towards the summit of Hirakimatā.

Just before the top, a hidden side-track plunges off down a slope and we arrive at a mossy clearing fringed by ferns, where a ramshackle cluster of timber and plywood buildings form Te Whare Huna - a Department of Conservation research hut and campsite.

A stack of plastic mugs and bowls stand drip-drying in a rusty dish rack on an outdoor bench. Limp washing hangs from a guy rope strung between two trees. Someone is brewing coffee at a damp-stained picnic table and the rising steam tangles with sunlight filtering through the leaves. I shuck my boots off and breathe in.

The DOC-funded survey 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.

A mix of researchers, volunteers, and staff have been here a week already, their second visit of the season. Late January is peak hatching season, and the team focuses on recording the breeding status of each burrow - whether it contains an egg or a chick, and the identity of the two parents, who typically pair for life.

Wildlife Management International staff member Cam Maclean, up here for his fourth season, hands a small laminated map to Emily Mowat, one of the newcomers.

"This is basically Biz's brain."

The map shows the contours of the summit, with red dots marking the location of the hundreds of study burrows.

There are GPS coordinates for each burrow too, but the map does the job, he tells Emily.

"You just use it for reference and it works pretty well."

Does Biz use the map?

"No. She does not need it."

Not only can Biz locate every burrow in the study, she can also tell you who normally nests there, the history of any previous tenants, and the best angle at which to stick your arm in to extract its reluctant occupants.

"I say to people, 'Oh, you go left at that tree and right there, and the burrow entrance is there, but if you go one metre to the left there'll be a hatch and it's deep, but the bird will sit to the left, and if you go past it he'll ambush you and bite your wrist,'" she says.

"But it's because I've been doing it for 29 years and these birds get into your blood. The mountain gets into your blood."

A species under threat

Even without the aid of Biz or her map, it's not difficult to find the petrels' burrows.

The hillside is booby-trapped with them, and even on the track into the campsite itself, Biz points out some pink tape on the ground that marks the top of a burrow lying just below the surface.

Almost every burrow the team checks houses someone: an adult incubating an egg, or a newly hatched chick.

The eggs are cream with a smattering of tan freckles, and slightly larger than a hen's egg.

The downy chicks look like balls of dryer lint and emit tiny, petulant honks like a squeaky dog toy.

The ease with which the team finds the birds, and the presence of eggs and chicks in most burrows, give the impression that this is a healthy, thriving species.

And although petrels only lay a single egg each year, the colony does have a high success rate. Each year about two-thirds of the burrows the study monitors are occupied by a breeding pair and, of those, nearly three-quarters will raise a fledgling.

But tākoketai are classified as nationally vulnerable, and their already small numbers are gradually declining.

There are no possums, goats or deer on Aotea, but ship rats, kiore, wild pigs, and feral cats all prey on petrels and their babies.

"Can you have a look at this, quickly?" Cam asks, appearing back out of the bush.

"I don't know if it's just hatched or if it's been predated."

He's holding a broken eggshell, a damp downy black feather still stuck to it.

Biz studies the shell's jagged edges.

"Nah, that's predated. That's rats eating a chick."

DOC has been trialling self-setting traps around the summit, which are doing a good job of reducing the number of ship rats, she says.

Cat-trapping efforts in nearby Okiwi Bay have also had benefits for the colony. An entire generation of feral cats that had learned to venture up the mountain in April and May when the chicks were fledging has been taken out.

Still, those gains are easily lost.

"If they stopped the control, we'd be in trouble."

The mystery that Biz is bent on solving, though, is what happens to the petrels when they leave the colony.

The final survey visit each season happens in April, to band the nearly-grown chicks before they start fledging.

When they launch themselves for the first time, they head straight across the Pacific, and don't return for an average of four years.

Most have never been seen again.

"We've banded over 5500 chicks over the 29 years and we've had less than 500 return," Biz says.

"Is that because we can't search this entire, massive island and they're somewhere else? Are they dying at sea? 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."

Long-line fishing is a particular threat to black petrels at sea, as their scavenging habits and diving proficiency make them vulnerable to getting hooked.

Back at the campsite, Victoria University masters student Maria Düssler peels the lid off a bright pink plastic container.

"Here's my pride and joy - my GPS devices."

Over two seasons, Maria has attached and then retrieved the stamp-sized, solar-powered devices from two dozen petrels. They record where the birds go and how deep they dive, which she then cross-references with fishing vessel tracks and logbooks.

"I actually recorded a record depth of them diving 38.5 metres, which is pretty damn impressive.

"You can see them following the vessel track. And then I wanted to see if their diving behaviour changed when they are around the fishing vessels."

Postdoctoral researcher Jamie Darby is using the same data, along with devices that detect light and acceleration, to determine whether artificial lighting on boats at night has any effect on the birds' diving behaviour.

"Long lines, particularly, are advised to set and haul at night-time, because it's thought that birds don't forage at night. But we know they do, so we wanted to see if that night-setting in conjunction with other methods will actually be effective."

Jamie only landed in New Zealand a few months ago from Cork University in Ireland, but he was aware of the Aotea black petrels long before he joined the survey.

"It's quite well-studied because Biz has put in such a shift.

"It's really hard to detect changes in population, steep declines, unless you have those long-term data, unless you're on the ground every year and seeing how each burrow is getting on."

After a week of sitting in the bush at night, waiting for the petrels to come back from days fishing at sea, the birds are no longer data in a spreadsheet.

"You're actually seeing all their little social lives going on. You have birds crashing in through the canopy of trees - they make quite a noise as they fall down, it's a bit of an intense way to get home - and then as they get to the ground, you hear their partners calling out from these burrows, just wondering, 'Are you home?'"

Unlikely allies

Biz knows well the power of seeing the birds firsthand, which is why, every year, she invites commercial fishers to volunteer.

She views them not as combatants, but collaborators.

"They're a little hesitant to begin with - you know, a bunch of scary scientists."

But show them a chick patiently waiting in a burrow for its parent to return from sea with some fish, and the perspective shifts.

"It's just the idea of them understanding, suddenly, that these seabirds are also just fishermen.

"Often that is a real lightbulb moment for the fishermen, when they realise, 'Oh, we're doing the same job.'"

It's also a practical way for the team to show them how to correctly handle a seabird.

"So if they do accidentally catch one and it's alive and they want to release it, it's how to hold it and how to disentangle it either from the net or the hook and then release it safely back to sea."

Recently-introduced regulations in New Zealand now require long-line fishers to use tori lines, which are lines set above the surface with bird-scaring streamers dangling from them; weighted hooks that sink before the birds can get to them; and set their lines at night, when the birds are less likely to be active.

WWF-New Zealand chief executive Kayla Kingdon-Bebb, who also joined the survey trip, says New Zealand can only control what happens within its own waters and fishing fleet, but the changes have made it easier to push for the same protections globally.

"If we're not walking the talk at home, it's very hard for us to go into an international forum and ask other foreign fleets, other countries, to pick up their game."

The massive increase in reported seabird and dolphin by-catch after the introduction of cameras on commercial inshore vessels in 2023 shows there is still work to do here, she says.

The number of dolphins reported caught jumped nearly seven-fold and interactions with albatrosses increased 3.5-fold.

The advocacy component of the Aotea survey, and Biz's empathy, are crucial to making that case for stricter rules to fishers.

"You can't change human behaviour if people don't understand that their actions are causing harm. So for Biz to have been bringing out commercial fishers and members of the seafood industry and others to show them why we're trying so hard to save these birds, it's very powerful."

A hundred-year hope

Biz's dream is for the project to outlast her.

"Basically you should be doing it intergenerationally, so the length of an adult plus the length of its first chick."

A petrel can live for 50 years - so the timeframe she has in mind is a full century.

Funding only comes in three-year tranches, though, and even that is a recent luxury. "It used to be yearly, which was very nerve-wracking."

The company itself has helped to keep the survey going through lean periods.

"I'm completely in love with these birds and so we do fund it ourselves at times, we do subsidise the research money."

We've paused at the very summit of Hirakimatā. Below us, olive-green bush stretches away to a bright harbour dotted with yachts. Further in the distance, Little Barrier, the home of the smaller colony, is a blue shadow on the horizon.

It's a view Biz has seen many times since she first came here as a 25-year-old. She hopes to still be seeing it when she's 90.

"This is an absolutely special place," she told me when I first arrived.

She also warned: "The birds will steal your heart."

I think back to the petrel I roused from its burrow that morning: its sleek head, the eye that met mine.

For Biz, there's no reason not to keep going; no reason not to slog up the track each season and plunge an arm into burrow after burrow, to see who has come back, who is incubating an egg, who has finally found a mate, and to hope - against the odds - for the first return of an elusive chick.

There's also no reason Great Barrier Island itself couldn't become a predator-free haven over the same timeframe, she says.

No rats, no cats, no pigs: just the whomph of a tākoketai through the canopy and the clownish slapping of its feet, as it waddles home to its burrow on the side of a mountain.

WWF-NZ paid for Kate Newton's flight to Great Barrier Island. The organisation had no oversight of this story.

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