Impossibly rare tropical bird swooped over California. Experts fear a trend.

A mysterious seabird swooping over the waters off San Clemente in recent weeks has wowed local birders. This species has likely never visited Orange County before.

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The California Bird Records Committee, a volunteer group with nine voting experts responsible for rare bird records, is investigating if the traveler is a lesser frigatebird, a tropical species.

There are only two previous confirmed accounts, one from 2025 and the other from 2007, of a lesser frigatebird showing up in California. These black-brown birds, which can spread their wings up to 6 feet and shine with a colorful gloss, are common in the southwest Pacific and Indian oceans but are exceedingly rare in the U.S.

“I might try to expedite this lesser frigatebird record because it’s so significant,” Thomas Benson, the secretary for the California Bird Records Committee, told SFGATE. “But it can take up to six months for an average record to get a decision.”

As the committee reviews photographs, audio recordings and written descriptions of the bird to make a determination, ornithologists in California are considering the potential implications of a lesser frigatebird’s arrival on local shores.

Ryan DiGaudio, an ecologist for Point Blue Conservation Science, said it was possible that the current extreme marine heat wave and brewing El Niño might have played a role.

“It’s not uncommon for unexpected seabirds to show up during exceptional oceanographic conditions — e.g. strong El Ninos or the current marine heatwave much of the Pacific is experiencing,” DiGaudio wrote to SFGATE. “Fish, krill, and other seabird food respond quickly to changes in ocean temps” and either die or “migrate to where their new ‘comfort zone’ is.” Seabirds in turn will travel “far across the ocean basins in search of their preferred food.”

He added that it’s “something we see when ocean temps are out of whack.”

Previously, individual lesser frigatebirds caught the keen eyes of U.S. birders not only in California but also Maine, Wyoming and Michigan. One recent report in Ohio is still under consideration.

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Peter Pyle, a staff biologist at the Institute for Bird Populations and a former member of the California Bird Records Committee, cautioned that it’s hard to draw conclusions from the behavior of just one bird. “I think in a lot of cases it’s just that an individual bird is a little cuckoo, you know, and it says, ‘Oh, I’m gonna go travel.’ It’d be like a human who suddenly wants to walk around the world.”

Yet Pyle noted that the suspected lesser frigatebird was one data point in a documented trend of tropical birds traveling northward as ocean temperatures warm. Additional rare sightings cropped up in just the last few days. A recent photograph captured what’s thought to be a red-billed tropicbird off Mendocino County, Pyle said.

And as birders searched high and low for the lesser frigatebird in San Clemente last weekend, by chance they spotted yet another tropical bird. Although it’s more common to see this bird — suspected to be a sooty tern — in California, the committee is now considering that identification, too, for the record.

“There is a pattern now,” Pyle said. He added: “Things are starting to pop up that suggest that maybe this tropical heat wave or developing El Niño is starting to show up here. It’ll be interesting to see what happens.”