Since mid-February, biologists have been struggling to control an outbreak of avian flu in a colony of more than 1,300 elephant seals at Año Nuevo, a state park 55 miles south of San Francisco. It’s the first time the virus has been detected in marine mammals in California, and so far, the outbreak has been linked to at least 30 seal deaths. Testing remains underway as scientists scramble to understand how the disease is spreading and what other species may be at risk. 

According to a new study, though, a local population of beloved peregrine falcons has likely been falling victim to the same strain for years. The study, published as a preprint on Feb. 14 by a team of scientists in Santa Cruz, Oakland, San Francisco and Idaho, has tracked the presence of falcons at dozens of nesting sites over 26 years. The research shows a precipitous decline of Bay Area peregrine falcons, including the suspected death last year of a famous bird who captivated audiences as they watched her raise her chicks atop UC Berkeley’s Campanile.

Because the study is just looking at nest occupancy, it likely underestimates the number of birds that have died from the virus.

Nest site occupancy has plummeted by 64% since 2022.

Bay Area peregrine falcon numbers began plummeting after a massive, global outbreak of avian flu in 2020, the study documents, with only about a third of the nesting sites still in use as of 2025. The news, while dire, nevertheless helps scientists understand how the disease is impacting local populations, and what we can expect for their recovery.

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“The depth of the data is something we’re really proud of,” Zeka Glucs, the director of the Predatory Bird Research Group at UC Santa Cruz and lead author of the study, told SFGATE. “And while the situation seems grim, as long as there are nests, there is hope.”

Avian flu — and in particular, the aggressive strain H5N1 — is caused by a virus that passes through direct contact with saliva or feces or through feeding on infected prey. Symptoms include tremors, lethargy and reduced or misshapen eggs, though some birds die suddenly without ever showing symptoms. 

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While bird flu has........

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