A persistent marine heat wave off the California coast has caused a significant die-off of seabirds, with many starving to death as their food sources are driven into deeper, cooler waters. Scientists are concerned that the recently formed El Niño could worsen the situation.
The warm ocean temperatures have decreased the band of cold, nutrient-rich surface water where small fish like krill, anchovies, and sardines thrive near the shore. This scarcity has led to widespread starvation among seabird populations, including California brown pelicans, loons, and grebes.
Marine ornithologists and volunteers conducting beach surveys have observed an alarming number of dead seabirds. Tammy Russell, a postdoctoral scholar at the Scripps Institution of Oceanography, described witnessing cormorants collapsing and dying within minutes of reaching the shore, a phenomenon she has not observed before. These surveys, conducted for decades, help establish a baseline for detecting threats to marine life.
Wildlife rehabilitation facilities reported treating hundreds of emaciated birds in the spring as the marine heat wave intensified. J.D. Bergeron, CEO of International Bird Rescue, stated that while dead birds on the beach are not unusual, the quantity seen this year is. He noted that brown pelicans are being found in unusual inland locations as they search for food, sometimes leading to injuries from fishing gear.
Many of the dead or debilitated seabirds examined have been young and emaciated. Tests for avian flu have largely come back negative, with some opportunistic infections appearing to be linked to malnourishment, according to the California Department of Fish and Wildlife.
Scientists with the U.S. National Oceanic and Atmospheric Administration confirmed the formation of an El Niño in June, predicting it could grow to historic strength and persist into 2027. El Niño is a natural warming of parts of the central Pacific that alters weather patterns globally and can elevate ocean temperatures.
While seabird die-offs occur periodically and are not always solely linked to marine heat waves, these events are becoming more frequent as the planet warms and oceans heat up. The current marine heat wave has persisted off the West Coast for about a year, marking one of the longest on record for such a large area, according to NOAA.
Records from Scripps Institution of Oceanography show that several coastal stations have registered record-breaking warm temperatures for extended periods this year. Robotic gliders operating offshore have also recorded high temperatures at depth, with anomalies in the spring comparable to those observed during the last El Niño in 2015.
This pattern of warming waters can disrupt marine food webs, impacting species from gray whales to seabirds as cold-water species move to deeper or more northerly regions. A similar phenomenon occurred a decade ago when a warm water mass, nicknamed "the blob," lingered off the West Coast for years, causing significant damage to marine ecosystems. This period overlapped with a strong El Niño in 2015, which coincided with one of the largest seabird die-offs recorded globally, particularly affecting common murres. These birds, with their high metabolism, can starve within days if they cannot find sufficient food.
Studies indicate that only a fraction of seabirds that die at sea wash ashore. It took years to confirm that an estimated 4 million common murres, more than half of Alaska’s population, died during "the blob" event, according to a 2024 study in the journal Science. The species is still experiencing challenges in recovering from that die-off.