Twenty years ago, David Grémillet, a seabird ecologist, watched in dismay as a heatwave hit a breeding colony of Cape gannets in Lambert’s Bay, South Africa, causing dozens of birds to keel over. An unseasonably hot wind sent temperatures to 40C (104F), too intense even for the heat-adapted birds.
While guarding their nests, they baked in the heat, says Grémillet, a researcher at the National Centre for Scientific Research in Montpellier, France. He and his colleague waded into the colony, picking up listless gannets and tossing them into the sea to cool down. Their frantic attempts saved a few, but in just under an hour, 100 birds died.
“When a seabird adult dies, you’re [also] losing all the young it could raise,” Grémillet says.
The fainting gannets were the first time Grémillet had witnessed how quickly birds could fall prey to high temperatures. In the two decades since, there have been several similar events. Colonies worldwide are experiencing sudden, large-scale die-offs, some killing thousands of seabirds at once
The world’s 359 seabird species have adapted to thrive across the oceans. Yet slow reproductive rates, narrow diets and the tendency to gather in exposed colonies, make seabirds extremely sensitive to environmental change.
Between 1950 and 2010, globally monitored populations plummeted by 70%. In the UK alone, nesting seabirds have declined by 30% since 2001. Seabirds are now counted as one of the most threatened groups of birds in the world.
Their numbers have been cut down by invasive species, overfishing, entanglements in fishing gear (bycatch), plastic pollution, oil spills and decades of habitat destruction.
But mass die-offs are adding to this already precarious situation. Experts have linked these deaths – which are separate to recent devastating outbreaks of bird flu – to bouts of hot weather, changing ocean currents and storms.
The seemingly increased frequency of these die-offs has left researchers scrambling to understand the losses, and worrying that already vulnerable seabirds are being dealt a devastating blow. “They’re being hit from all sides,” says Grémillet.
Thick-billed murres have been dying in their nests on hotter days in the Arctic, which is warming at least twice as fast as elsewhere on the planet.
More than 354 Magellanic penguins perished in an Argentinian colony on one day in early 2019 as temperatures in the shade reached 44C, the hottest there since records began in 1982.
Climate change not only brings another layer – it’s also intensifying other problems
Maria Dias, conservation ecologist
One of the worst mass die-offs started in the summer of 2015. The north Pacific began mysteriously belching up waves of dead common murres on to the shores of California and Alaska. A huge patrol effort counted 62,000 beached murres, some washing up while still in their death throes.
“That sort of struggle, up close and personal, is awful to watch,” says Julia Parrish, a marine scientist at the University of Washington.
The event was one of the largest ever “wrecks” – a phenomenon where an unusually large number of dead seabirds wash up over a short period. The murres were found to be emaciated, and researchers drew links between these deaths and an unprecedented warming event out at sea months before.
In 2014, a gigantic blob of warming water had begun forming in the north-east Pacific, caused partly by slower winds reducing the turnover of seawater, leaving more of it exposed to the sun. The resulting “marine heatwave” changed the abundance and type of phytoplankton in the north-east Pacific, with the effects rippling up the food chain to the fish species on which seabirds depend.
“It’s like if you went to the grocery store and there was food but you didn’t recognise it,” says Parrish, who co-authored a study about the die-off. The warm water also increased the appetites of predatory fish, meaning more competition for the limited prey.
Across a swath of ocean “the size of continental Canada”, this tepid water changed the menu for the millions of seabirds who migrate there to feed, Parrish says. It is believed that thousands of seabirds simply starved because of these changes in their food source.
The north Pacific heatwave lingered for more than two years, killing an estimated one million seabirds.
Several confounding factors and a lack of long-term population studies make it difficult to attribute individual die-offs solely to climate change, says Maria Dias, a conservation ecologist at the University of Lisbon. But it is clear it is playing a significant role.
Acute weather extremes are increasing as the world heats up, and the climate crisis has already been linked to a doubling of marine heatwaves. Climate change now poses the third-biggest threat to seabirds (after seabird bycatch and the severe impact of invasive species – such as rats), according to research led by Dias.
“Climate change not only brings another layer, it’s also intensifying other problems,” she says. For example, by altering food webs, climate change amplifies the effect of overfishing on seabirds.
Warming and the rise in sea levels also increase the intensity of storms. High winds can send nests hurtling into the ocean. Wild waves can create a “washing-machine effect” that is thought to push fish beyond some seabirds’ reach.
We lose a lot of penguin eggs and chicks because the parents just leave their nests
Katta Ludynia, South African researcher
Seabirds have always suffered mortalities in storms, but recurring wrecks over short periods can dramatically undermine slow-breeding species such as the European shag. On the east coast of Scotland, which holds some of the UK’s largest shag colonies, storms have destroyed up to 85% of that local population in one go, says Francis Daunt, an animal population ecologist at the UK Centre for Ecology & Hydrology.
“We are concerned about whether these [eastern] populations might go extinct over the course of this century,” Daunt says.
Such momentous seabird losses have a ripple effect. Seabird colonies deposit vast amounts of nutrient-rich guano across the land and sea; if this declines, so could the health of some forests and coral reefs, which rely on this nourishment.
Seabirds are “powerful indicators of the state of the oceans”, says Grémillet. When they struggle, it means stress for other animals beneath the waves, and signals systemic threats to an ecosystem on which humans also depend.
These threats do not always result in huge numbers of deaths. Extreme weather events are rooted in climate changes, which chip away at seabird populations in slower but no less destructive ways. Shifting ocean currents are relocating fish, forcing birds into longer foraging trips, a process that taxes their bodies and undermines their ability to breed.
Predicted changing wind currents could affect the foraging success of migratory birds such as albatross, some species of which are already experiencing high “divorce” rates due to breeding failures linked to warming waters that have altered food supply.
Meanwhile, endangered Cape penguins in southern Africa, whose populations have declined by almost 65% since 1989, are breeding later in the year to keep in step with the shifting availability of fish.
This means the penguins are incubating their eggs in mid-summer when rising annual temperatures make them too hot to stay put, says Katta Ludynia, research manager at the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB). “We lose a lot of eggs and chicks because the parents just leave their nests.”
Temperature shifts can also change the availability of prey for newborn chicks. Atlantic puffins are experiencing breeding failures because populations of sand eels, their preferred prey, are declining, in part due to the climate crisis. The UK could see a decline of 90% in puffin numbers by 2050 as ocean temperatures continue to increase.
Meanwhile, rising sea- levels rise threaten to shrink seabird nesting habitat worldwide.
Climate mitigation is essential to saving seabirds and other species but it will not bring changes quickly enough to help those most threatened, Parrish says. That is why many bird researchers and conservationists are focused on helping seabirds adapt.
In South Africa, SANCCOB is working with the South African National Parks authority to rehabilitate naturally shady nesting habitat, and even exploring colony-wide misting to cool down the seabirds on hot days. Each summer, SANCCOB also stages routine rescues of several hundred eggs, to be hand-reared and later released.
Experts also want to decrease other pressures such as overfishing, bycatch and invasive species, Parrish says, to give seabirds “more breathing room” in the face of the climate crisis.
More data on changing marine and seabird health could inspire better conservation measures. In 2021, conservationists drew up a huge high-seas marine protected area in the north Atlantic after BirdLife International collated years of tracking data, revealing that roughly 5 million seabirds congregated in this region to feed.
“If we can protect these areas, we can build resilience in species to cope with climate change,” says Dias, who was involved in the project.
But seabird declines may continue to be precipitous. Grémillet says this has caused him to develop “a form of eco-grief” but, he says, continuing to study seabirds is crucial to saving species. His mission is “to bring testimony to people about these beautiful creatures, and what we’re about to lose”.
This article by Emma Bryce was first published by The Guardian on 5 September 2022. Lead Image: A dead gannet on a beach in Pembrokeshire, Wales. A heatwave in South Africa caused a mass die-off in a colony of Cape gannets that first alerted some ecologists to the effect rising temperatures were having on seabirds. Photograph: Manor Photography/Alamy.
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