There is a ray of hope for the vanishing orange-and-black Western monarch butterflies.

The number wintering along California’s central coast is bouncing back after the population, whose presence is often a good indicator of ecosystem health, reached an all-time low last year. Experts pin their decline on climate change, habitat destruction and lack of food due to drought.

An annual winter count last year by the Xerces Society for Invertebrate Conservation recorded fewer than 2,000 butterflies. The amount is a massive decline from the tens of thousands tallied in recent years and the millions that had clustered in trees from Northern California’s Mendocino County to Baja California, Mexico, in the 1980s. Now, their roosting sites are concentrated mostly on California’s central coast.

This year’s official count started Saturday and will last three weeks, but already an unofficial count by researchers and volunteers shows there are more than 50,000 monarchs at overwintering sites, said Sarina Jepsen, director of endangered species at the Xerces Society.

“This is certainly not a recovery, but we’re really optimistic and just really glad that there are monarchs here and that gives us a bit of time to work toward recovery of the Western monarch migration,” Jepsen said.

Western monarch butterflies head south from the Pacific Northwest to California each winter, returning to the same places and even the same trees, where they cluster to keep warm. The monarchs generally arrive in California at the beginning of November and spread across the country once warmer weather arrives in March.

Scientists don’t know why the population increased this year, but Jepsen said it is probably partly due to better conditions at their breeding grounds.

The Western monarch butterfly population has declined by more than 99 percent from the millions that overwintered in California in the 1980s because of the destruction of their milkweed habitat along their migratory route as housing expands into their territory and use of pesticides and herbicides increases.

Researchers also have noted the effect of climate change. Along with farming, climate change is one of the main drivers of the monarch’s threatened extinction, disrupting an annual 3,000-mile migration synced to springtime and the blossoming of wildflowers.

Monarch butterflies lack state and federal legal protection to keep their habitat from being destroyed or degraded. Last year, they were denied federal protection, but the insects are now among the candidates for listing under the federal Endangered Species Act.

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