Marine ornithologist Tammy Russell, walking along Blacks Beach in San Diego, discovered multiple feathered carcasses within minutes—some mixed with kelp, others under rocks. These grim findings are part of monthly surveys conducted by scientists and volunteers to assess the impact of a massive marine heat wave that has lingered off parts of the California coast for months.
Record Ocean Temperatures and Starvation
Record-setting ocean temperatures have reduced the band of cold, nutrient-rich surface water where krill, anchovies, and sardines thrive near the shore, leading to starvation deaths among seabirds such as California brown pelicans, loons, and grebes, said Russell, a postdoctoral scholar at the University of California, San Diego’s Scripps Institution of Oceanography. “We’ve been seeing cormorants walk to shore and then just die within the hour. One time it happened within 15 minutes, and I’ve never seen that before,” Russell said. “That has been heartbreaking for me and we’re seeing this happening across the whole coast.”
El Niño Threatens to Worsen Conditions
Scientists fear the die-off could worsen with the recently formed El Niño, a natural warming of parts of the central Pacific that alters weather worldwide and spikes global temperatures. The US National Oceanic and Atmospheric Administration confirmed in June that an El Niño has formed and is expected to grow to historic strength. While not all seabird deaths off California this year are tied to the marine heat wave, such die-offs are becoming more frequent as the planet warms and oceans heat up.
“We don’t know how bad this is going to get,” said Russell, who has written about five species of Booby that are now common off California due to warming ocean temperatures.
Marine Heat Wave Persists
A marine heat wave has persisted off parts of the west coast for the past year, marking only the third time on record that such a large section of coastal waters stayed warm for so long, according to NOAA. Scripps measures daily ocean temperatures at 10 coastal stations along the California coast, with records stretching back over a century. This year, three stations broke records for 40 days or more, said director Melissa Carter. Robotic underwater gliders with sensors also recorded high temperatures offshore and at depth during the spring. Dan Rudnick, who runs the Scripps glider program, said the warm temperature anomaly off southern California this spring was comparable to that during the last El Niño in 2023, and this was before the formation of this year’s El Niño, which could stretch into 2027.
Disrupted Food Webs
As cold-water species move deeper and farther north, the marine heat wave coupled with El Niño could further disrupt food webs for sea life from gray whales to seabirds, a pattern similar to a decade ago. Wildlife rehabilitation facilities treated hundreds of emaciated birds this spring when the marine heat wave intensified. JD Bergeron, CEO of International Bird Rescue, said, “It’s not abnormal to see dead birds on the beach, but the quantity of dead birds is unusual.” Brown pelicans have been turning up in inland lakes. “When birds starve, especially the pelicans, they start to look in unusual places for food,” Bergeron said. “They will chase fishing boats, they will go to piers, and you end up with birds with fishing line and fishhook injuries.”
Young Birds Most Affected
Many dead or debilitated seabirds examined this year have been young and emaciated, and most have tested negative for avian flu, according to the California Department of Fish and Wildlife. Some had opportunistic infections linked to malnourishment. Krysta Rogers, a senior state environmental scientist, noted that high mortality rates among young Brandt’s cormorants and common murres began after a robust 2025 breeding season, peaking post-winter, and appeared to coincide with the marine heat wave. Those deaths may be mostly due to chicks not surviving on their own, but she does not discount the heat wave’s effect, considering an increase this spring in reported deaths from other species and not just young ones. The US Fish and Wildlife Service, which collects data from the dead seabird surveys, said they do not yet have a comprehensive report ready.
Historical Context: The Blob and Past Die-Offs
Only a fraction of birds that die at sea wash ashore. In 2013, a warm water mass nicknamed “the blob” developed off Alaska and stretched south, lingering for years and wreaking havoc on marine ecosystems all the way to Mexico’s Baja California peninsula. One of the strongest El Niños on record overlapped with it in 2015. Carcasses of emaciated common murres appeared on beaches in what biologists say was the largest seabird die-off recorded in the world’s oceans. Common murres have a high metabolism and must eat prey matching 10% to 30% of their body mass daily; they can reach a critical starvation threshold within three days. Studies show that only a fraction of birds that die at sea wash ashore. It took years for scientists to confirm that more than half of Alaska’s population of common murres—an estimated 4 million birds—died during “the blob,” according to a 2024 study in the journal Science. The species is still struggling to recover.
