Marine heat wave drives seabird deaths along California coast, surveys show

Scientists and volunteers surveying California beaches have been finding unusually large numbers of dead seabirds. Marine ornithologist Tammy Russell said many birds appeared starved during months of very warm ocean conditions. Researchers warned the problem could grow as El Nino develops. Officials also stressed that not every death is linked to the heat wave.

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Long-running surveys by several organisations track dead seabirds and other sea life that wash ashore. The work helps build baseline data and spot new threats over time. Russell said recent beach checks showed a "grim assessment\" of the effects of a prolonged marine heat wave. The warm water has lingered off parts of California’s coast for months.

Marine heat wave and El Nino drive seabird die-offs

US National Oceanic and Atmospheric Administration confirmed in June that an El Nino formed. NOAA said it is expected to grow to historic strength. Scientists said die-offs happen at times, and some 2026 deaths have other causes. Still, warming seas are linked to more frequent seabird die-offs as oceans heat up.

NOAA said a marine heat wave has stayed off parts of the US West Coast for about a year. It was only the third time on record such a large area stayed warm so long. Russell said higher temperatures reduced the cold, nutrient-rich surface band near shore. That change cut food for krill, anchovies and sardines.

Russell, a postdoctoral scholar at the University of California, San Diego, Scripps Institution of Oceanography, described rapid bird deaths. \"Weve been seeing cormorants walk to shore and then just die within the hour. I mean one time it happened within 15 minutes, and Ive never seen that before,\" Russell said. \"That has been heartbreaking for me and were seeing this happening across the whole coast.\"

Russell said the shifting ocean is also changing which species appear offshore. Russell has written about five species of Booby now common off California. Russell added: \"We dont know how bad this is going to get.\" Scientists said cold-water species may move deeper and farther north, disrupting food webs from gray whales to seabirds.

Scripps marine heat wave data show record ocean temperatures

Scripps measures daily ocean temperatures at 10 coastal stations along California. Director Melissa Carter said records extend back more than a century. Carter said three stations broke records for 40 days or more this year. Staff gathered samples from piers using insulated buckets and from surfers, lifeguards, and rocky shore teams.

Robotic underwater gliders also logged high temperatures offshore and at depth during spring. Dan Rudnick, who runs the Scripps glider programme, said the warm anomaly off Southern California was comparable to the last El Nino in 2023. Rudnick said this occurred before this year’s El Nino formed. Scientists said El Nino could stretch into 2027.

International Bird Rescue and wildlife officials track seabird die-offs

Wildlife rehabilitation facilities treated hundreds of emaciated birds this spring as the heat wave strengthened. J D Bergeron, CEO of International Bird Rescue, spoke in May about the beach counts. \"Its not abnormal to see dead birds on the beach, but the quantity of dead birds is unusual,\" Bergeron said in an interview.

Bergeron said hunger was pushing seabirds into risky areas. \"Brown pelicans are turning up in inland lakes,\" Bergeron said. \"When birds starve, especially the pelicans, they start to look in unusual places for food,\" he said. \"They will chase fishing boats, they will go to piers and you end up with birds with fishing line and fish hook injuries.\"

California Department of Fish and Wildlife said many affected birds examined this year were young and emaciated. The department said most tested negative for avian flu. Some birds had opportunistic infections linked to malnourishment. Officials said starvation signs matched reports of reduced prey close to shore during the marine heat wave.

Krysta Rogers, a senior state environmental scientist, said other factors may also be involved. Rogers said high deaths among young Brandts cormorants and common murres followed a robust 2025 breeding season. Those deaths peaked after winter and appeared to coincide with the heat wave. Rogers said chicks may have failed to survive alone.

Rogers said the heat wave still could be hurting other seabirds. Rogers pointed to increased spring reports involving other species, not only young birds. The US Fish and Wildlife Service, which gathers data from the beach surveys and other sources, said it did not yet have a comprehensive report ready. Scientists also noted many birds die at sea unseen.

Common murres and past marine heat wave die-offs

Researchers compared the current event with a major warm period a decade ago. In 2013, a warm water mass called the blob formed off Alaska. It then stretched south and lingered for years, affecting ecosystems to Mexico’s Baja California peninsula. One of the strongest El Ninos overlapped in 2015, worsening ocean disruption.

Biologists said emaciated common murres washed ashore then in huge numbers. They described it as the largest seabird die-off recorded in the world’s oceans. Common murres resemble thin penguins and can fly far to find small fish. They also dive and swim nearly 600 feet, or 183 metres, to catch prey.

Scientists said murres need frequent feeding because of high metabolism. If murres do not eat prey equal to 10 per cent to 30 per cent of body mass daily, they can burn fat quickly. Researchers said birds can reach a starvation threshold within three days. This helps explain how sudden food shortages can cause mass deaths.

Studies also show most birds that die at sea never reach the beach. It took years to confirm the blob’s scale, according to a 2024 Science study. Scientists concluded more than half of Alaska’s common murres died, about 4 million birds. Researchers said the species is still struggling to recover as warm-water events return.

Along California’s coast, researchers said beach surveys are giving early warnings about the current marine heat wave. Officials said the data still do not prove one cause for every death. Even so, multiple agencies linked widespread emaciation to reduced nearshore prey. Scientists said they will keep tracking conditions as El Nino develops.

With inputs from PTI