Marine ornithologist Tammy Russell, who works at the University of California, San Diego’s Scripps Institution of Oceanography, walked along a San Diego beach and was confronted with a disheartening sight. Various dead seabirds lay among washed-up kelp and under rocks. This grim discovery highlights the severe effect of a prolonged marine heat wave along the California coast.

Each month, scientists and volunteers monitor beaches to track seabird mortality. These surveys, conducted by different organizations for many years, help establish data on beached sea life, identifying threats and impacts.

Seabirds such as California brown pelicans, loons, and grebes have largely perished due to starvation. Record-high ocean temperatures have shrunk the cold, nutrient-rich surface layer where krill, anchovies, and sardines thrive close to shore. Russell reported instances of cormorants walking to the shore only to die shortly after, highlighting a troubling crossing point.

Scientists worry this situation could worsen. A recently confirmed El Nino event adds to concerns. This natural climate pattern warms parts of the central Pacific, altering weather worldwide and further heating ocean temperatures.

We don’t know how bad this is going to get, said Russell, emphasizing the unpredictability of these changes.

Monitoring data shows that die-offs like this occur periodically. Not all seabird deaths off California this year directly link to the marine heat wave. However, increasing ocean temperatures correlate with more frequent die-offs. NOAA’s data illustrate that the current extended marine heat wave is one of the rare significant events on record along the West Coast.

Director of the Scripps program, Melissa Carter, noted records of unprecedented ocean temperatures at various coastal stations. Robotic underwater sensors also detected abnormal temperatures offshore.

Wildlife rehabilitation centers like SeaWorld San Diego have treated numerous emaciated birds as the heat wave intensified. Brown pelicans, in particular, searched for food in unusual locations, increasing their risk of injuries.

The California Department of Fish and Wildlife examined many young and malnourished deceased seabirds. Other factors may contribute to these die-offs, but increasing numbers of birds failing to survive on their own align with the warmer ocean temperatures.

Past events, including a massive warm water mass dubbed “the blob” in 2013, showed similar consequences. Many seabirds succumbed during overlapping El Nino occurrences.

Common murres exemplify the vulnerability of seabirds. They require substantial food intake due to high metabolism, and failing to catch enough prey results in their rapid decline. Research shows that a small proportion of birds that die at sea are discovered on shore. Challenges faced by populations during past events, like the one affecting common murres in Alaska, indicate difficulty in recovery.

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