First Cases of Bird Flu Confirmed in Northern Elephant Seals in California

California wildlife officials have confirmed the first known cases of highly pathogenic avian influenza, or bird flu, in northern elephant seals, raising new concerns about the virus’s spread among marine mammals along the U.S. West Coast.

Seven recently weaned elephant seal pups at Año Nuevo State Park, about 20 miles north of Santa Cruz, tested positive for the H5N1 strain of highly pathogenic avian influenza (HPAI), according to confirmation from the U.S. Department of Agriculture’s National Veterinary Services Laboratory on Feb. 25, 2026.

The discovery marks the first time the virus has been detected in marine mammals in California and the first documented cases in northern elephant seals anywhere.

Rapid Detection at a Key California Wildlife Site

Researchers first noticed unusual symptoms in seals on Feb. 19 and 20, including breathing problems, weakness, and tremors. Samples collected from sick and dead animals were analyzed at the University of California, Davis, where initial screening identified avian influenza. Federal testing later confirmed the H5N1 strain.

“This is exceptionally rapid detection of an outbreak in free-ranging marine mammals,” said Christine Johnson, director of the Institute for Pandemic Insights at UC Davis’ veterinary school. She credited coordinated monitoring efforts for identifying what are likely the earliest cases.

Scientists had increased surveillance in recent years as bird flu spread widely across North and South America, devastating wildlife populations. In 2023, the virus caused significant die-offs among southern elephant seals in Argentina, heightening concerns about the vulnerability of related species.

Roxanne Beltran, a University of California, Santa Cruz professor who leads the park’s elephant seal research program, said researchers were specifically watching for early warning signs.

“Given the catastrophic impacts observed in related species, we were concerned about the possibility of the virus infecting northern elephant seals for the first time,” Beltran said.

Colony Monitoring Intensifies as Park Closes Public Access

Año Nuevo State Park hosts one of the largest mainland breeding colonies of northern elephant seals in the United States, with about 5,000 animals during peak season. Approximately 1,350 seals were present when the outbreak began.

In response, California State Parks temporarily closed public viewing areas and canceled guided elephant seal tours for the remainder of the breeding season while officials assess the threat.

The site is uniquely suited for disease monitoring. For more than 60 years, UC Santa Cruz researchers have tracked individual seals using flipper tags, allowing scientists to observe health changes over time.

Federal and state agencies—including NOAA Fisheries, the California Department of Fish and Wildlife, and the West Coast Marine Mammal Stranding Network—are now working together to monitor the situation.

Despite the outbreak, researchers say there is cautious optimism.

“Most of the adult females had already departed the beach for their routine migrations before the outbreak began, and most seals on the colony seem healthy,” Beltran said.

Public Health Risk Remains Low, Officials Say

While H5N1 can infect humans, health officials say the risk to the general public remains very low.

Still, experts are urging beachgoers to keep their distance from seals and other wildlife.

People should not touch live or dead marine mammals or allow pets to approach them, as this can increase the risk of disease transmission and harm vulnerable animals.

Anyone who encounters a sick, injured, or dead marine mammal along the coasts of California, Oregon, or Washington should contact NOAA’s West Coast marine mammal stranding hotline rather than attempting to intervene.

Bird Flu’s Global Spread Raises Ongoing Concerns

The H5N1 virus was first identified in 1996 in domestic geese in Southeast China. Over the past three decades, it has spread globally through poultry and wild bird populations, reaching North America in late 2021.

Since then, outbreaks have been confirmed in nearly every U.S. state and Canadian province, affecting commercial poultry farms, backyard flocks, wild birds, and multiple mammal species. Human infections, while rare, have also been documented.

Marine mammal outbreaks in the U.S. have previously been reported in Maine in 2022 and Washington state in 2023, both linked to transmission from infected birds.

Scientists Expand Surveillance to Prevent Wider Impact

The latest cases highlight the importance of wildlife disease monitoring, particularly as viruses cross species barriers.

Researchers at UC Davis and partner institutions are expanding surveillance efforts using new tools such as drones and advanced sensors to track wildlife health more effectively, especially in remote coastal areas.

Teams will continue weekly updates, testing, and aerial surveys to monitor the colony and detect any further spread.

A Critical Moment for Wildlife Health Monitoring

The detection of bird flu in California’s northern elephant seals underscores how quickly infectious diseases can move into new species and ecosystems.

While most of the colony appears healthy for now, scientists say ongoing monitoring will be essential to understand the virus’s impact and protect both wildlife and public health along America’s Pacific coast.

John Irving

“Certified food guru. Internet maven. Bacon junkie. Tv enthusiast. Avid writer. Gamer. Beeraholic.”