SAN FRANCISCO — California's Monarch butterflies -- whose appearance in winter is a celebrated show of color and beauty that draws tourists from around the world -- have dwindled in numbers this year, and may be in the midst of a longer-term decline.
"Our numbers are dramatically fewer," said Sarah Hamilton of the Ventana Wilderness Society, a group that counts the orange and black butterflies as they spend the winter clustering in California's coastal groves of eucalyptus, pine and cypress.
In Monterey County, south of San Francisco, Hamilton's counts have found only about a third as many butterflies this winter as last. And some of her group's counts hint that Monarch populations may have been declining for several years, although nobody knows why.
But even with the diminishing numbers, tourists are still flocking to the California coast to see the insects, said Ro Vaccaro, president of the Friends of the Monarchs in Pacific Grove, a town so crazy about the little creatures that it has a Butterfly Parade, a Monarch Avenue and a $1,000 city fine for anyone who molests a Monarch.
"The ones that made it are looking pretty good," Vaccaro said.
Monarchs are famous for both their beauty and stamina.
East of the Rocky Mountains, the butterflies make an extraordinary annual migration of thousands of miles, flying from summer habitats in the United States to wintering grounds in Central Mexico.
In California, the butterflies generally make a shorter journey, flying from the Central Valley to the Pacific Coast, but they are still popular with tourists and nature-lovers.
Volunteers spend hours peering through binoculars trying to count the butterflies as they huddle together, a difficult task that makes a precise count impossible.
"We try to count their feet and divide by six, but that doesn't always work," Vaccaro joked.
Still, the best estimates show a decline.
Dennis Frey, professor of biological sciences at Cal Poly San Luis Obispo, estimated that there might be only 1 million Monarchs in California's 300 wintering sites this year, down from roughly 1.5 million last year and perhaps the lowest count in a decade.
In Pacific Grove, an annual Thanksgiving count at a key habitat site has shown a steady decline since 1997, Hamilton said.
The reason for the longer-term drop remains a mystery, but Frey thinks that this winter's butterfly shortage may be due to a late-winter drought last year. The lack of rain meant less milkweed, the summer plant where the butterflies lay their eggs and which then becomes their only food source as caterpillars.
Less summer milkweed means fewer winter butterflies, experts said.
"It takes a fat, juicy caterpillar to make a beautiful, healthy butterfly," Vaccaro said.