Songbirds are dying across parts of California and the Pacific Northwest, and officials think crowds at bird feeders are to blame, according to recent news reports.

The California Department of Fish and Wildlife (CDFW) and wildlife rehabilitation centers have been "inundated" with calls since December 2020 from California residents reporting that they found sick or dead finches at their bird feeders, according to a statement posted Feb. 8.

An investigation into the deaths revealed that the birds were infected by the Salmonella bacteria and had developed salmonellosis. A tale as old as (pandemic) time: large gatherings were to blame.

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Finches who came into contact with food, water or objects contaminated with feces from infected birds can contract the illness, according to the statement. As more birds gather in an area such as a bird feeder or a bird bath, the risk of infection increases.

Most birds die within a day of being infected, Krysta Rogers, an avian disease specialist with the CDFW, said in the statement. Almost all of this year's outbreak were reported in places with bird feeders.

The outbreak especially affected pine siskins (Spinus pinus), a species of finch that's small, brown with a sliver of yellow, streaked and very chatty (Its calls sound like a "like a zipper being zipped," according to ebird.org.) But lesser goldfinches (Spinus psaltria), American goldfinches (Spinus tristis) and others were also affected. Most of these salmonellosis cases were along the Central Coast, in the San Francisco Bay Area and in the Sierra Nevada.

Infected birds look lethargic, puffed or fluffed up with partially closed eyes (and sometimes with swollen, red or irritated eyes), according to Sonoma County's Bird Rescue Center.

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"Salmonellosis occurs periodically in pine siskins in some winters throughout their range," Rogers said in the statement. However, this year's outbreak is particularly bad because it's an "irruption year" of pine siskins. There's a lot of pine siskins that have traveled south due to a shortage of seeds in Canada, according to the Bird Rescue Center of California's Sonoma County and The National Audubon Society.

Because pine siskins can spread the bacteria, salmonellosis outbreaks are often correlated with irruption years, according to the Bird Rescue Center. If you find a sick or dead bird, officials recommend contacting your local wildlife rescue center immediately. They also recommend keeping young children or free-roaming cats and dogs away from infected equipment or dropped seeds.

But "the very best way" to stop the birds from spreading the bacteria is to remove the bird baths and feeders so that the birds can spread out and feed on natural vegetation, according to The Bird Rescue Center. The Center "strongly recommends" removing the feeders and birdbaths from your yard until next spring when the Pine Siskins migrate north once again.

But the outbreak isn’t solely contained to California, dead and sick birds are also turning up in the Pacific Northwest. The Washington state Department of Fish and Wildlife has also urged people to take down their bird feeders until at least April 1.

Editor's Note: This story was updated to include that the outbreak is also happening in the Pacific Northwest.

Originally published on Live Science.