Source: University of Auckland – UoA
Studies this summer show seabirds in the Hauraki Gulf are struggling to raise chicks, as the impacts of climate change hit.
Lack of food appears to have caused poor chick survival for some seabird species in the Hauraki Gulf this summer.
University of Auckland Associate Professor Brendon Dunphy, research fellow Dr Edin Whitehead and master’s student Isabella Brown have been monitoring the nests of diving petrels and fluttering shearwaters in the gulf since October last year.
The outlook for these seabirds is bleaker than expected, say the researchers from the School of Biological Sciences and Centre for Climate, Biodiversity and Society.
Whitehead says there was a 50 percent failure rate in the 13 fluttering shearwater nests she monitored at Tāwharanui, north of Auckland. That failure rate is higher than normal, she says.
Four of the adult shearwaters abandoned their nesting boxes, typically a sign they can’t find enough food to survive and feed their chicks, Whitehead says.
In 2019, fluttering shearwaters in the gulf were foraging and returning to the nest daily, but in December 2025, they were disappearing for as long as 12 days. The adult birds left their nests for so long, Whitehead feared the colony had been wiped out.
“GPS tracking showed they were covering huge distances, making foraging trips as far as North Cape, which is more than 200 kilometres away,” says Whitehead.
The parents usually rotate shifts, with one sitting on the egg, while the other flies out to sea seeking food, then swapping every day or two.
“But if there's not enough food, the parent sitting on the egg might get too hungry to stay and will go to sea to feed too.
“It slows down the development inside the egg, because it’s cooler for longer periods,” says Whitehead.
Fluttering shearwater chicks in the gulf usually hatch between late October and the end of November, but this year hatching didn’t begin until late November. Some shearwaters were sitting on eggs until mid-December, possibly because the eggs had been left to cool more often while the parents searched long distances for food.
“This is unusually late and concerning because it's so different from what's been previously recorded for the species in the Hauraki Gulf,” says Whitehead.
Brown also observed diving petrel chicks hatching up to a month later than usual on Tiritiri Matangi Island.
Lower than average weights were recorded among the 15 diving petrel chicks monitored on Tiritiri.
“They were a lot lighter than normal when they departed, so they had less energy reserves and that could reduce their survival rate,” says Brown.
Dunphy says seabirds are sensitive to changes in the ocean, offering an early warning sign of shifts that will affect other species in the Hauraki Gulf.
“The ocean has absorbed 25 billion Hiroshima bombs worth of energy since the 1960s, but we’re now seeing the point where the ocean can no longer absorb more.
“We’re experiencing frequent marine heatwaves, which have immediate effects on the fish, zooplankton and krill that the diving petrels and fluttering shearwaters feed on.
“When marine heatwaves affect zooplankton, that affects the whole food web above it. We’re seeing the impacts on seabirds, because they are easy to observe, but everything in the gulf will be affected,” he says.
The Hauraki Gulf is a global seabird hotspot, where about 70 species breed and forage. Five species breed nowhere else in the world.
“We’re hoping some species will be able to cope with the higher ocean temperatures, but the ones we’ve looked at, it’s had quite a dramatic impact,” Dunphy says.
“I would like to say we can turn it around, but we’re living with 1.5 degrees of global warming. The goal is to keep it to that, but we’re already starting to overshoot it.”
Whitehead says slashing the amount of fishing in the gulf would help, particularly commercial fishing with purse seine nets that strip life from the sea.
Big boils-ups in the gulf used to occur often, with large fish, such as trevally and kahawai, pushing small fish and zooplankton to the surface, where seabirds could feast.
But these days, boil-ups are reported to have dwindled in size and frequency, making it harder for seabirds to find enough food to feed themselves and growing chicks, Whitehead says.
Dunphy says coastal marine reserves work wonders, but many of the schools of large fish that push prey to the surface are migratory.
In order to protect the migratory fish so vital to seabird survival, marine protection would need to be mobile and seasonal. GPS tracking could indicate where seabirds are feeding and where temporary protection is needed.
Brown says a diving petrel fledging rescued on Waiheke Island this summer weighed about 90 grams, when it should have weighed 140.
“The people at Waiheke Native Bird Rescue said they could feel its ribs. It was just wasted away,” she says.
Dunphy says “eco-grief” affects the seabird researchers.
“Our job is to study the effects of climate change on seabirds, but that doesn’t make it easier,” says Whitehead.
Dunphy says he had imagined climate change might have impacted heavily on the gulf by the end of his career, but it has struck earlier.
“We're transitioning to a different Hauraki Gulf, a certain amount of change is going to be inevitable.
“But we can make the gulf as naturally resilient as it would be without the other human impacts, like sedimentation, pollution and overfishing,” he says.
The seabird monitoring was carried out with Catalyst funding from the Royal Society Te Apārangi and the support of the George Mason Centre for the Natural Environment.
