SAN FRANCISCO — The number of western monarch butterflies wintering along the California coast has plummeted precipitously to a record low, putting the orange-and-black insects closer to extinction, researchers announced Tuesday.

An annual winter count by the Xerces Society recorded fewer than 2,000 butterflies, a massive decline from the tens of thousands tallied in recent years and the millions that clustered in trees from Northern California’s Marin County to San Diego County in the south in the 1980s.

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.

On the eastern side of the Rocky Mountains, another monarch population travels from southern Canada and the northeastern United States across thousands of miles to spend the winter in central Mexico. Scientists estimate the monarch population in the eastern U.S. has fallen about 80% since the mid-1990s, but the drop-off in the […]