CALIFORNIA — A persistent marine heat wave off the California coast has led to mass seabird die-offs, with scientists and wildlife rehabilitators reporting widespread starvation. Marine ornithologist Tammy Russell found dead seabird carcasses on a San Diego beach, and wildlife rehabilitation facilities have treated hundreds of emaciated birds this spring.

California brown pelicans, loons, and grebes have starved to death in recent months. Many dead or debilitated seabirds examined this year have been young and emaciated. Russell, a postdoctoral scholar at the University of California, San Diego, Scripps Institution of Oceanography, described observing cormorants die rapidly after reaching shore. "We've been seeing cormorants walk to shore and then just die within the hour. I mean 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," she said.

Record-setting ocean temperatures have reduced the band of cold, nutrient-rich surface water near the shore where krill, anchovies, and sardines thrive. Three Scripps coastal stations broke temperature records for 40 days or more this year. Robotic underwater gliders also recorded high temperatures offshore and at depth during the spring. The warm temperature anomaly off Southern California this spring was comparable to that during the last El Nino in 2023.

The U.S. National Oceanic and Atmospheric Administration confirmed an El Nino formed in June, and it is expected to grow to historic strength. This present marine heat wave marks the third instance on record that such a large part of coastal waters has remained warm for an extended period, according to NOAA. In 2013, a warm water mass known as "the blob" developed off Alaska, stretched south, and persisted for years. One of the strongest El Ninos on record overlapped with "the blob" in 2015, leading to carcasses of emaciated common murres appearing on beaches.

J.D. Bergeron, CEO of International Bird Rescue, noted the unusual quantity of dead birds. "It's not abnormal to see dead birds on the beach, but the quantity of dead birds is unusual," Bergeron said. Brown pelicans are now appearing in inland lakes. Bergeron explained that starving birds, particularly pelicans, seek food in unusual locations. "When birds starve, especially the pelicans, they start to look in unusual places for food," he said. This behavior can lead to additional injuries. "They will chase fishing boats, they will go to piers and you end up with birds with fishing line and fish hook injuries," Bergeron said.

High mortality rates among young Brandt's cormorants and common murres began after the 2025 breeding season and peaked post-winter. Most examined seabirds have tested negative for avian flu, according to the California Department of Fish and Wildlife, though some had opportunistic infections linked to malnourishment. Scientists and volunteers conduct monthly surveys of dead seabirds off the California coast, and the U.S. Fish and Wildlife Service collects this data but does not yet have a comprehensive report on the deaths. "We don't know how bad this is going to get," Russell said.