Most people know that monarch butterflies spend the winter in huge clusters in Mexico. Fewer know that monarchs from west of the Rocky Mountains winter at a few dozen sites along the California coast. A U.S. Fish and Wildlife Service public affairs specialist, who grew up in Minnesota watching her father raise monarchs from eggs and caterpillars gathered from the milkweed in their yard, drove up the coast with her camera to see them for the first time, and to show them to people who cannot go: monarchs are declining, and she hoped the pictures might move people to plant milkweed or join a citizen science project.
Monarchs cannot fly with wet wings; this one waits out the rain in Santa Cruz. U.S. Fish and Wildlife Service.
Clustering for winter
The butterflies spend the cool months clustered in trees, sheltering from cold and rain until spring brings milkweed and flowers. They arrive in October and gather on pine, cypress and eucalyptus. The town of Pacific Grove is so famous for them it is nicknamed "Butterfly Town, U.S.A."
A monarch on a cedar branch in Santa Cruz. U.S. Fish and Wildlife Service.
Clusters are also when scientists count them. In one Monterey cypress in Santa Cruz, Service biologists estimated 11,000 monarchs, a number that sounds encouraging, but overall the population is falling.
About 11,000 monarchs in one Monterey cypress in Santa Cruz. U.S. Fish and Wildlife Service.
Clustered with wings closed, monarchs show their drab undersides and look like dead leaves, some protection from predators. Up close, the clusters are full of color.
Monarchs in Pacific Grove, looking like dead leaves. U.S. Fish and Wildlife Service.
A cluster at the Monarch Butterfly Sanctuary, Pacific Grove. U.S. Fish and Wildlife Service.
Weather rules their days
- Rain. On wet days they barely move; they must wait for their wings to dry. They can survive freezing and some rain, but not for long.
- Temperature. They can fly above about 60 °F, or 50 °F in sun.
- Wind. If wind or rain disturbs a site, they fly off to form a new cluster under better cover.
- Sun. On sunny winter days they leave their clusters to bask until the cool of dusk.
Waiting out wet weather. U.S. Fish and Wildlife Service.
Forming a new cluster after the wind shifted. U.S. Fish and Wildlife Service.
Sunbathing on a winter day. U.S. Fish and Wildlife Service.
Why they are declining
Monarchs have wintered on the West Coast and in Mexico for centuries, and they are remarkably resilient. But habitat loss, more frequent extreme winter storms and drought, and other human-caused threats are driving them down.
A tree covered in monarchs. U.S. Fish and Wildlife Service.
A tagged traveler
One butterfly in a cluster carried a small white tag: monarch AM288, tagged by a citizen scientist in Providence, Utah, on 26 September 2016 and spotted on 4 December 2016 at its wintering site in Ventura, about 655 miles away. According to the Southwest Monarch Study, it was the first Utah-tagged monarch ever found in California. Citizen scientists can help track the western monarchs' still-mysterious movements.
Monarch AM288, tagged in Utah and found in California. U.S. Fish and Wildlife Service.
Sources
- U.S. Fish and Wildlife Service, "Virtual Tour: Visiting the Winter Home of Western Monarch Butterflies"; rewritten in hubnx's own words. Photographs: U.S. Fish and Wildlife Service.
Licence: CC0 1.0 (public domain) · Adapted from www.fws.gov
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