California Monarch Campaign

When Monarch butterflies come up in conversation, we usually think of the 3,000-mile journey they make between Canada and Mexico east of the Rockies. These Monarchs return each winter to roosts in the hills of Michoacan, Mexico, where they gather by the millions. What people often do not realize is that over a million Monarchs also make a western migration. Monarchs west of the continental divide overwinter along the coast of California and breed on milkweed as far north as British Columbia. Although the western winter roosts are not as large as their Mexican counterparts, these magical places may contain tens of thousands of butterflies. Many of these West Coast sites are open to the public.

Many of these sites are threatened by development and loss of the trees that create the unique conditions required by these resting butterflies. The Xerces Society, in cooperation with other conservation groups in California, has worked to protect these sites and offered expertise regarding their management.

Western Monarch Migration
Two main populations of Monarchs exist in North America: one population is east of the Rocky Mountains, and the other is west of the Rocky Mountains. There has been recent evidence that suggests that these populations may intermix.     

The western population of Monarchs makes a migration similar to its eastern counterpart, but overwinters instead at more than 200 coastal sites along the California coast, from north of San Francisco south to the Mexican border. Tens of thousands of individuals may be present at an individual Monarch grove.

The Monarchs that migrate away from these overwintering sites in the spring move up into California’s Central Valley and Sierra Nevada foothills, and north to Oregon and Washington. By the end of the summer, after three generations have passed, some offspring can reach as far north as British Columbia. Although only one to two million Monarchs migrate back to California’s coastal groves in the fall (as opposed to 100 million to Mexico), the western Monarchs are still important.

Eastern Monarch migration
The Monarch butterfly migration east of the Rocky Mountains is one of the world’s magnificent natural events. Adult Monarchs that emerge from their chrysalis in early fall will fly from the United States and Canada to overwintering grounds in Mexico, some traveling as far as three thousand miles. These are the only butterflies in the world to make such a long, two-way migration each year.

In the fall, Monarch butterflies from east of the Rocky Mountains return to high-altitude oyamel fir forests in central Mexico. It is here that they spend the winter in dense aggregations. These Monarchs begin migrating north in March and early April to the Gulf Coast of the southeastern United States, where the females lay their eggs on milkweed plants. One to two generations of Monarchs are produced in the Gulf Coast States in the spring. These offspring of the wintering generation continue northward without their “mothers”, where they recolonize the northern breeding range. Because southern milkweed plants die in June, the migration must continue north in order to utilize the milkweed resources of central and northeastern North America. This allows Monarchs to produce up to three additional summer generations. The cycle begins again in the fall when this new generation of Monarchs heads south.

Despite this unique life history, neither the United States nor Canada has protected any habitat along the major migration corridors for Monarchs. Mexico has protected only tiny fragments of the habitat to which the Monarchs migrate. Because so little protection is afforded these butterflies, the annual migration of the Monarch in North America has been recognized as an endangered biological phenomenon.

Basic biology
The Monarch, indigenous to the New World, occurs throughout North and South America. It also has established breeding populations in Australia, a number of Atlantic and Pacific Islands including Hawaii and Bermuda, and the eastern coast of Spain.     

Monarchs lay their eggs on milkweed plants (genus Asclepius). The caterpillars that hatch from the eggs feed on the milkweed leaves, incorporating the plant’s toxic compounds (cardiac glycocides) into their bodies. As the caterpillars grow, they become more and more distasteful to potential predators. They usually pupate near the plants on which they feed. When the Monarchs emerge as adults, they either continue migrating to the north and east or turn around and start the journey back to their overwintering grounds, depending upon the time of year.

Unlike the Mexican sites whose main threats are logging and conversion to marginal crop land, the sites in California are threatened by the large sums of money to be made by coastal land development. Also, natural aging and death of the trees in many groves is leaving breaks in the canopy, gaps that make the canopies unsuitable for butterflies in the winter. The situation in California is further confounded because most of the Monarchs overwinter in non-native Australian Eucalyptus trees, the removal of which is a major target of restoration along the coast.     

In the United States, most of the Californian winter roosting sites are not protected, although several are located within state, county, or town parks. Some California coastal counties have enacted ordinances to protect winter roost trees, and the California state government allocated $2 million for acquisition of Monarch winter habitat. Outside of the overwintering sites, however, neither Monarchs nor their habitat and primary host plant, milkweed, are protected. To the contrary, milkweed is often targeted with herbicide as a weed.

Conservation efforts
If you live in California, you can help conserve California Monarchs by     

  • Planting native milkweed and nectar sources and encouraging local businesses, friends, and vineyards to do the same
  • Helping protect small natural areas that support milkweed patches or overwintering sites
  • Contacting the California Coast Commission and let them know that Monarchs are an important resource that need to be protected
  • Participating in the annual Thanksgiving Monarch counts, so that we can track the status of their populations over time
  • Donating to the Xerces Society and earmark your funds for the California Monarch Campaign
Please remember that we are most interested in counts of monarch groves conducted during the week around Thanksgiving and New Years day. If you can conduct surveys of monarch groves in addition to these times, it would be great. Thank you for your efforts on behalf of monarch butterfly conservation in California.     

survey instructions
survey form
Thanksgiving count survey data from 1997-2006

Where to see Monarchs in California
The mild winters of the California coast are a perfect haven from the harsh cold weather in our country’s interior. Monarchs take advantage of this climate and use the same overwintering sites year after year. Congregations of overwintering Monarchs are found at more than 200 sites along the California coast, from Mendocino County in the north to San Diego in the south. Here is information on several overwintering sites that are open to the public. Find the sites closest to you and plan for a magical day exploring this amazing phenomenon. Please keep in mind that Monarchs are present from October through February. Also, a few of these sites host festivals or other events.     

Monarch Grove Sanctuary, Pacific Grove
Pacific Grove is home to the Monarch Grove Sanctuary. Each winter, about 20-30,000 Monarch Butterflies cluster together on the pines and eucalyptus of the Sanctuary. Arriving in October, these hardy insects will overwinter until February, when they will join the spring Monarch migration, spreading northward and eastward as they hunt for milkweed plants on which to lay their eggs.

Directions: The Sanctuary is located on Ridge Road, one block west of the intersection of Lighthouse Avenue and 17 Mile Drive. Parking is available at the entrance.

Natural Bridges State Beach, near Santa Cruz
The park Monarch Grove provides a temporary home for over 100,000 Monarchs each winter. The Monarch Grove has been declared a Natural Preserve, thus protecting the Monarchs and their winter habitat from human encroachment or harm. This is the only State Monarch Preserve in California. Access to the preserve is limited to a wheelchair-accessible boardwalk and observation area.

Directions: Take Swift Avenue west from Highway 1, or follow West Cliff Drive north along the in-town bluffs until it ends at Natural Bridges.

Lighthouse Field State Beach
Also known as Point Santa Cruz, this area forms the northern boundary of Monterey Bay. It is one of the last open headlands in any California urban area. Surfers, tourists, birds, and wintering Monarch butterflies are drawn to this area. Sea lions populate the offshore rocks.

Directions: The beach is on West Cliff Drive in downtown Santa Cruz, just south of Natural Bridges State Park.

Pismo State Beach, near San Luis Obispo 
Pismo State Beach offers all kinds of attractions: hiking, swimming, surf fishing, and digging for the famous Pismo clam. There are tree-lined dunes and the beach is popular with bird watchers. The park has the largest over-wintering colony of Monarch butterflies in the U.S.

Directions: The beach is located in the town of Oceano off Highway 1.

Point Lobos State Park, near Carmel 
Monarchs found in warm protected areas along Whaler’s Knoll Trail.

Directions: Three miles south of Caramel on Highway 1.

Ardenwood Historic Farm
The Monarchs roost in the North Woods between the RR tracks and the northern fence boundary.

Directions: The Farm is located south of Interstate 88 (Hwy 17) and north of Hwy 84 (which leads to Dumbarton Bridge).

Ellwood Main 
This is the premier Monarch site in southern California, with close to 100,000 Monarchs in good years.

Directions: East of Santa Barbara in the town of Goleta (UCSB), take the Glen Annie/Storke Road exit.

Morro Bay State Park
Situated in scenic Morro Bay in San Luis Obispo County, the Park contains several butterfly overwintering sites. The camp ground is closed to camping until spring of 2005.

Directions: From San Luis Obispo take Highway 1 north to the Los Osos – Baywood Park off ramp. Turn left, go about 1 mile and turn right into the Park.

City of San Leandro
The City of San Leandro sponsors monarch tours for the public at the Monarch Golf Course.
Information about small additional sites


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Program Features
Program Highlights
  • • The Xerces Society has awarded two $3,750 Joan M. DeWind awards for research into lepidoptera conservation
  • Butterfly-a-thon pledges raise $30 per species that Bob Pyle observes for butterfly conservation work
Additional Information
El Segundo Blue butterfly (Euphilotes bernardino allyni) by Larry Orsak


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