Northern California bears found with same troubling symptoms under investigation in Tahoe bruins

A mysterious complex of symptoms that has shown up sporadically in young black bears in the Tahoe Basin in recent years has now appeared in two severely underweight yearlings found in Northern California over the past five weeks.

The sickly youngsters, both euthanized and found to have brain inflammation, or encephalitis, were found about 15 miles apart in east Humboldt County and just across the county line in Trinity County in late February and early March.

A third bear, perhaps a sibling, was observed in the same area Wednesday, exhibiting similar symptoms, though it hadn’t been captured yet, said Monte Merrick, director of Humboldt Wildlife Care Center near Arcata, which received the first two.

The animals were the first known cases outside the Tahoe area to display shared symptoms, chiefly encephalitis, documented since 2014, when the Nevada Department of Wildlife first raised the red flag about young bears with neurological abnormalities in the region, officials said.

Fewer than 20 cases from both sides of the state line have been examined since, most from the Tahoe Basin, which has a large black bear population and ample opportunity for human encounters, experts said.

But the pace of discovery has increased in the past 1½ years, in part, perhaps, because “we’ve really been looking,” said Brandon Munk, senior wildlife veterinarian with the California Department of Wildlife’s Wildlife Investigations Laboratory in Rancho Cordova, where he started in 2016.

“Once you start looking, you start finding,” Munk said. “So long story short, we really don’t have a baseline to say how prevalent this has been.”

Most of the afflicted bears have been about a half or a third the size they should be at a year old — though not as undersized as those that passed through Humboldt County. Many have an odd gait or head tilt, tremors or other neurological symptoms, as well as dull, unresponsive demeanor or fearless, “dog-like” behavior toward people.

Researchers increasingly focused on the issue have discovered five previously unknown and unidentified viruses in tissue samples from some of those bears, as well as from others available for various reasons. Two of the five viruses were pervasive.

The type of inflammation is suggestive of a virus, Munk said, though scientists are a long way from linking the symptoms to any particular source and have not ruled out other causes. It’s also unknown if the bears had suppressed immune systems for other reasons and then succumbed to viruses or maladies that wouldn’t otherwise have proven fatal, or if their cases are only showing up now because of increased human interaction with wildlife.

“This could be linked to urbanization, but then at the same time there could be bears out in the wild that have had this and we just haven’t seen them,” said Sanchez, with the Nevada Department of Wildlife.

Denise Upton, animal care director with Lake Tahoe Wildlife Care in South Lake Tahoe, said animals with the syndrome remain rare, but it’s hard to tell sometimes because humans are so negligent about leaving out trash and other attractants or even feeding bears directly that they become habituated to people.

In the meantime, her organization has increasingly treated and released severely underweight cubs still young enough to be with their mothers but who weren’t, for some reason. Those animals including four early last year that clearly had been out all winter on their own, but that did not demonstrate neurological deficits or other significant problems, Upton said.

“We don’t know what happens out in the forest,” Upton said. But a starving cub that sees a person “won’t show fear because hunger overrides their fear.”

“My question is ’What’s happening to all of their mothers?’ ” she said.

The two bears taken in by the Humboldt County wildlife center were found roaming near neighborhoods in Willow Creek and Salyer, about 260 miles north of Santa Rosa, Merrick said.

They were both about a quarter and one-eighth the expected weight for their age — about a year old — with acute skin conditions, Munk said.

The female, captured Feb. 27 at a mere 10 pounds — the size a cub would normally be before it’s even weaned, Merrick said — was initially considered for rehabilitation at Sonoma County Wildlife Rescue, one of three wildlife rehab centers licensed by the state. Then Munk got a look at a photograph of her.

“I said, ’Eeeeeee. I know what this is, and it has a poor prognosis,’ ” he recalled.

The animal was transferred to the investigative lab and later found to have slight encephalitis, though observation of her before she was put down did not reveal outward signs of neurological trouble, Munk said.

The larger bear, a male, captured March 13, had a slight but rapid head tremor and collapsed in his enclosure when he was put inside, said Merrick.

“It was remarkable because a yearling bear, you should not be able to pick up and handle by yourself,” he said. “Even at 25 pounds, he should have been hard to handle. But he wasn’t.”

The animal was euthanized by the state before he was transferred to the Wildlife Investigations Lab, where a postmortem exam revealed the encephalitis, Munk said.

In between, the agency came by another sick bear that had turned up at a utility site in Pollack Pines, in El Dorado County, where workers found it unfazed by attempts to shoo it away, spokesman Peter Tira said The animal seemed lethargic and unbothered when they yelled or clapped at it. It found a more comfortable home in a residential backyard, where, in direct contradiction of expert guidance, the residents fed it fruit and gave it water, and the bear even jumped into the trunk of a car at one point.

A warden who went to investigate determined “the bear just didn’t seem quite right, (was) walking oddly, dull and not responsive like a normal bear should be,” Tira wrote in a recent account of the incident.

During a week of observation in the lab, the bear — at 21 pounds, about a quarter what it should weigh — also displayed intermittent head tremors and a subtle head tilt that Munk recognized as similar to neurological symptoms exhibited by others. Encephalitis was discovered during the postmortem exam.

The American black bear’s range includes the Sierra Nevada and much of Northern California, including Sonoma and Napa counties, particularly the Mayacamas Mountains, where their presence has been increasingly documented in recent years with the rise of motion-activated camera networks.

Lone bears often are seen making forays into settled valley neighborhoods, as well, particularly during spring, when the 1- and 2-year-olds are leaving their mothers for the first time, learning to hunt and forage and staking out their own territories.

Members of the North Bay Bear Collaborative, created to avoid human/bear conflicts so that bears can remain wild and unharmed, said they were unaware of any bears seen in the area with apparent neurological issues.

Most observations come through wildlife cameras anyway, said John Roney, manager at Sugarloaf Ridge State Park.

But bears have been sighted all over the county in the past year, said Meghan Walla-Murphy, a wildlife ecologist and lead on the collaborative, turning up regularly on cameras at Sugarloaf and nearby Pepperwood Preserve, around Napa County and in west Sonoma County, in areas like Stillwater Cove and Willow Creek.

“They’re generally very skittish,” Roney said. “We’ve got plenty on the cameras. For the most part around here, they are staying away from humans.”

You can reach Staff Writer Mary Callahan at 707-521-5249 or On Twitter @MaryCallahanB.

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