While guarding their nests, they baked in the heat, says Grémillet, a researcher at the National Center for Scientific Research in Montpellier, France. He and his colleague entered the colony, picking up limp hooks and throwing them into the sea to cool off. Their frantic efforts saved a few, but in less than an hour 100 birds died. “When an adult seabird dies, you are [also] losing all the young people it could grow,” says Grémillet. The fainting mushrooms were the first time Grémillet saw how quickly birds could fall victim to high temperatures. In the two decades since then, there have been several similar events. Colonies around the world experience sudden, large-scale die-offs, some killing thousands of seabirds at once A cape wagtail with his chick. Photo: Eduard Drost The world’s 359 species of seabirds have adapted to thrive in the oceans. However, slow reproductive rates, narrow diets, and a tendency to congregate 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 considered one of the most threatened bird groups in the world. Their numbers have been reduced by invasive species, overfishing, entanglement in fishing gear (entanglement), plastic pollution, oil spills and decades of habitat destruction. But the mass deaths add to this already precarious situation. Experts have linked these deaths – which are distinct from recent devastating bird flu outbreaks – to hot spells, changing ocean currents and storms. Graph showing the factors that are the main cause of decline for seabirds. Climate change is third The seemingly increased frequency of these deaths has left researchers scrambling to make sense of the losses and worrying that already vulnerable seabirds are being dealt a devastating blow. “They are being hit from all sides,” says Grémillet. Rough mulberries die in their nests on the hottest days in the Arctic, which is warming at least twice as fast as anywhere else on the planet. More than 354 Magellanic penguins perished in a colony in Argentina on one day in early 2019 as temperatures in the shade reached 44 degrees Celsius, the hottest there since records began in 1982. Climate change not only brings another layer – it also intensifies other problems Maria Dias, conservation ecologist One of the worst mass eruptions began in the summer of 2015. The North Pacific mysteriously began to pick up waves of dead common mullets off the coasts of California and Alaska. A massive patrol effort counted 62,000 noises on the beach, some of which washed up while still in death throes. “This kind of fight, up close and personal, is awful to watch,” says Julia Paris, a marine scientist at the University of Washington. The event was one of the largest ‘wrecks’ of all time – a phenomenon where an unusually large number of dead seabirds wash up in a short period of time. The pockets were found to be emaciated and researchers had linked these deaths to an unprecedented warming phenomenon in the sea months before. In 2014, a giant blob of warm water had begun to form in the northeast Pacific, caused in part by slower winds that reduce the circulation of seawater, leaving more of it exposed to the sun. The resulting “sea heat” changed the abundance and type of phytoplankton in the northeast Pacific, with the effects rippling up the food chain in the fish species on which seabirds depend. “It’s like going to the grocery store and there’s food but you don’t recognize it,” says Parrish, who co-authored a study on die-off. Warm water also increased the appetites of predatory fish, meaning more competition for limited prey. Magellanic penguins at the Punta Tombo reserve in Chubut province, Argentina, where hundreds died in extreme heat in 2019. Photo: Reuters In a strip of ocean “the size of continental Canada,” this warm water has changed the menu for the millions of seabirds that 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 heat wave persisted for more than two years, killing an estimated one million seabirds. Dead victims washed up on a rocky beach in Whittier, Alaska in 2016. More than 60,000 victims died in the 2015-16 North Pacific ‘wreck’. Photo: Mark Thiessen/AP Several confounding factors and a lack of long-term population studies make it difficult to attribute individual deaths solely to climate change, says Maria Dias, a conservation ecologist at the University of Lisbon. But it is clear that it plays an important role. Extreme weather events are increasing as the world warms and the climate crisis has already been linked to a doubling of sea heat waves. Climate change is now the third biggest threat to seabirds (after seabird bycatch and the severe impacts of invasive species – such as rats), according to research led by Dias. “Climate change not only brings another level, it also intensifies other problems,” he says. For example, by altering food webs, climate change amplifies the effect of overfishing on seabirds. Warming and rising sea levels are also increasing the intensity of storms. Strong winds can blow nests into the ocean. Wild waves can create a “laundry effect” that is believed to push fish beyond the reach of some seabirds. We are losing a lot of eggs and penguin chicks because the parents are just leaving their nests Katta Ludynia, South African researcher Seabirds have always suffered mortality in storms, but repeated wrecks over short periods of time can dramatically undermine slow-breeding species such as the European tern. On the east coast of Scotland, home to some of the UK’s largest barnacle colonies, storms have wiped out up to 85% of this local population in one go, says Francis Daunt, an animal population ecologist at the Center for Ecology & Hydrology at United Kingdom. “We are concerned about whether these [eastern] Populations may become extinct within this century,” says Daunt. Such significant seabird losses have a ripple effect. Seabird colonies deposit vast amounts of nutrient-rich guano across land and sea. If this declines, so could the health of some forests and coral reefs, which rely on this food. Seabirds are “powerful indicators of the state of the oceans,” says Grémillet. When they struggle, it means stress for other animals below the waves and signals systemic threats to an ecosystem on which humans also depend. These threats don’t always result in massive death tolls. Extreme weather events are rooted in climate change, which is wiping out seabird populations in slower but no less devastating ways. Changing ocean currents carry the fish away, forcing the birds on longer foraging journeys, a process that taxes their bodies and undermines their ability to reproduce. A black-browed albatross and its chick are nesting in the Falkland Islands. More albatross breeding pairs are separated due to feeding problems as changing wind currents affect foraging. Photo: Andy Rouse/PA Projected changing wind currents could affect the foraging success of migratory birds such as the albatross, some species of which are already experiencing high rates of “divorce” due to breeding failures linked to warming waters that have altered the food supply. Meanwhile, endangered Cape penguins in southern Africa, whose populations have declined by almost 65% since 1989, breed later in the year to keep up with changing fish availability. This means the penguins incubate their eggs in mid-summer, when rising annual temperatures make them too hot to stay, says Katta Ludynia, research manager at the South 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 changes can also alter the availability of prey for newly hatched chicks. Atlantic puffins are facing breeding setbacks because populations of sand eels, their preferred prey, are declining, in part due to the climate crisis. The UK could see a 90% decline in puffin numbers by 2050 as ocean temperatures continue to rise. Meanwhile, rising sea levels threaten to shrink seabird nesting habitat worldwide. An Atlantic tern swims in the Sept-Îles nature reserve in western France. The species is experiencing reproductive failures as its preferred prey, sand eels, decline in numbers. Photo: Loïc Venance/AFP/Getty Climate mitigation is necessary to save seabirds and other species, but it won’t change quickly enough to help those most threatened, Parrish says. That’s why many bird researchers and conservationists are focusing on helping seabirds adapt. In South Africa, SANCCOB is working with the South African National Parks Authority to restore natural shady nesting habitats and even explore colony-wide misting to cool seabirds on hot days. Every summer, SANCCOB also organizes routine rescues of several hundred eggs, which are to be hand-reared and later released. Experts also want to reduce other pressures such as overfishing, bycatch and invasive species, Parrish says, to give seabirds “more breathing room” in the face of the climate crisis. In South Africa, African penguin eggs are rescued and the chicks are hand-reared before being released to increase numbers in wild colonies. Photo: SANCCOB More data on changing marine and seabird health could inspire better conservation measures. In…
