The number of western monarch butterflies has hit a historic low for the second year in a row, raising fears that California’s populations are in peril and may not recover.

Only 29,418 monarchs were counted at 240 sites along the state’s coast, according to the annual Thanksgiving tally released Thursday by the Xerces Society for Invertebrate Conservation, a nonprofit that conducts the annual census.

That’s fewer than 15% of the insects recorded several years ago, when 200,000 to 300,000 of the orange and black butterflies flew to coastal California, clustering and clumping on trees. In 1997, 1.2 million were counted.

About 2,200 more butterflies were found than in the previous year’s count — but that’s not a meaningful difference because it is the result of greater survey effort, with volunteers visiting more sites, according to the Xerces Society.

As habitats shrink, populations are teetering on the threshold — 30,000 insects – that scientists think are needed to keep the population from collapsing, said Xerces biologist Emma Pelton.

“We hope we’re wrong – that they bounce back,” said Pelton. “If we’re right, we’ll know in two years, when they’re gone and we can’t bring them back.”

In the past five years, at least 20 monarch resting sites have been significantly damaged or destroyed, according to Pelton. These sites — even the same trees — are where monarchs get food and shelter after spending the summer in the Sierra Nevada, Oregon and Washington. Four more sites are currently threatened by development and a large number of sites need restoration.

Several of these lost sites are in the San Francisco Bay Area, including Yerba Buena Island. Santa Cruz County lost three sites and San Luis Obispo County lost six sites. Habitat was also damaged at Gaviota State Beach, based in Santa Barbara County.

People unwittingly destroy the monarchs’ homes when they cut or trim eucalyptus trees, said Pelton. These trees provide food and shelter to the butterflies during the winter months.

Some trees are removed for home construction. Others because they are believed to pose a greater fire threat than native species of plants and trees or because homeowners fear falling branches will damage property, she said.

It’s not known how butterflies choose their winter homes, where they have never been before. The butterflies now in coastal California are the descendents of insects that left last spring and laid eggs along their route to the Sierra Nevada, Oregon, Washington and highlands of Arizona. Monarchs produce four to five generations a year, each with their own own urge to move.

Last fall’s counts in Alameda County found 31 butterflies at Albany Hill, up from 12 last year but down from 1,000 at their peak in 1997. There was 1 butterfly at Fremont’s Ardenwood Historical Farm, down from 66 last year and 25,000 in 1997. San Leandro Golf Course showed a rebound from last year, up to 702 from 192. But that’s far less than its peak of 25,000. Only two butterflies were seen at Contra Costa County’s Point Pinole, up from one last year and down from its peak of 5,000.

In Santa Cruz County, 1,997 butterflies were counted at Natural Bridges State Park, up from 1,120 last year but far below the peak of 120,000. Monterey County’s famed Pacific Grove had 642 butterflies this year, down from 815 last year and 45,000 at its peak.

There is new research that suggests western monarchs are genetically linked to eastern monarchs, a finding that buoys hope for the resilience of the iconic species.

If the western monarchs vanish, perhaps their eastern insects could be introduced to our state, according to butterfly experts at the first-ever Western Monarch Summit in Carmel earlier this month. It is possible that our butterflies originally flew here from the east.

But it’s too soon to conclude that the DNA of eastern and western monarchs is identical, or that eastern monarchs would replicate the spectacular migratory phenomenon that we see here every fall and spring, according to Emory University biology professor Jacobus de Roode, who is completing work on a major study of the monarchs’ genomes.

Protection of habitat — through state laws that shield wintering sites and encourage conservation — is the best way to boost numbers, according to the Xerces Society. It encourages the federal government to list the monarch butterfly as an endangered species.

“They need legal protection — not just ‘on the book,’ but in practice,” said Pelton.

This year, Xerces will partner with California State Parks, Fiscalini Ranch, and the USDA Natural Resources Conservation District to restore monarch habitat in the Central Valley and at wintering sites along the coast. It also aims to work with native seed producers to increase the availability of milkweed, a butterfly food source.

“Do not lose heart. At least the population did not diminish any further,” said Robert Coffan of Western Monarch Advocates, a new nonprofit that links people committed to restoring the butterfly’s population.

“We are learning what the problems and drivers are. We have collectively identified so many ways to help. We are becoming more galvanized,” he said. “We are working more collectively.”

Learn more about helping western monarchs: savewesternmonarchs.org

Contribute sightings of monarchs and milkweeds to the Western Monarch Milkweed Mapper: monarchmilkweedmapper.org