On California Coast, Monarch butterflies seek winter refuge in oceanside forests

If you take the road less traveled along the Pacific Coast, you will find yourself on the narrow, winding, two-lane Highway 1, which meanders through a collection of small California towns, along ocean cliffs and beaches.

Here you’ll find travelers who are focused more on the journey and less on reaching their destination, and there are rewards in store for those who do.

Driving lazily along this route in November, there are places where your eyes might convince you that the laws of nature no longer apply. Leaves of orange and brown appear to be defying the rules, drifting not down with the force of gravity, but sidewise and upward among the groves of eucalyptus trees rooted in the sandy soil.

Santa Cruz, Pacific Grove, Big Sur and Pismo Beach are among many hidden gems along the route where this phenomenon exists. It is worth pulling over and getting out of your car to explore.

Closer examination will reveal that those were not fall’s leaves, but thousands of migratory Monarch butterflies! They hang in vast numbers, resembling a cluster of dried leaves to the untrained eye. At Pismo Beach, a very nice state park, a cadre of enthusiastic docents invites the passer-by to stop a while and marvel.

Closer examination through available spotting scopes reveals tens of thousands of butterfly wings layered like shingles on a roof, providing protection from cold temperatures and seasonal rains.

But what draws them to this place where flowers seem few and conditions seem harsh? The microclimate provided by the grove of trees itself is the key.

Monarch butterflies have long been known as migratory insects, traveling thousands of miles from overwintering sites in Mexico, and up the eastern side of the United States. Monarchs have evolved to be completely dependent on milkweed for egg-laying and caterpillar development, and migrate to states where milkweed grows in the wild.

What is less known is that another subset of Monarchs has evolved to make a parallel migration along the western coast of North America, wintering in the protective groves of trees found in quiet coastal towns of California, and migrating north each summer on the west side of the Rockies to northern states that support milkweed plants.

There are distinct differences between these two migratory populations. Whereas Monarchs from Mexico tend to live for about six weeks, Monarchs from the Pacific Coast of California may live up to six months!

Nevertheless, the Monarchs who leave the overwintering sites in California to travel north will not live to return. It is their descendants who somehow know to head to the groves utilized by their forbearers. The trees provide the much-needed shelter from the winds, a place to cluster and develop mutual protection from rain, and an opportunity to find mates.

Although most of the groves where overwintering occurs in California are largely made of eucalyptus trees, studies have shown that Monarchs do not prefer this invasive species. They have simply adapted to what is available.

Indeed, when given a choice, they seem to prefer native conifers much of the time, but are known to switch between tree species as conditions change. Overall, they did not cluster on one tree species significantly more frequently than another, indicating that Monarchs do not prefer eucalyptus — or any tree species — all of the time.

However, more often than not, Monarch butterflies clustered significantly more than expected on native trees, particularly at midseason when the weather was most inclement. They also clustered disproportionately on native conifers when the overwintering population size was highest. At most sites monarchs exhibited tree switching, shifting from eucalyptus to native conifers in the middle or late winter. — http://digitalcommons.calpoly.edu/theses/1256/]

With this knowledge, docents and volunteer gardeners at the Pismo Beach Monarch Butterfly Grove have, in recent years, begun a program of planting more native cypress trees in the grove. As the mature eucalyptus trees die out, more native options will be available to future generations of Monarchs.

Without the microclimate created by a grove of trees at this place, the location of which is somehow, mysteriously transferred to future generations of butterflies, the Monarch populations will decline, as they have been doing worldwide. The local volunteers are determined that it will not be for lack of a healthy grove of trees in Pismo Beach.

Once again, it’s all about the trees.

Just the facts

• The Pismo Beach Monarch Grove is on Highway 1 at the southern edge of Pismo Beach, and is active with butterflies from November through March.
• This is one of the largest colonies of monarchs in the United States, attracting an average of 25,000 butterflies to an area of less than an acre.
• The site is handicapped accessible with wide compacted gravel pathways.
• Well-trained and enthusiastic volunteer docents are on hand to offer informative talks and answer questions from 10 a.m. to 4 p.m. during the active season, as well as offering scheduled talks, and providing spotting scopes for close viewing.
• A small gift shop is on site selling Monarch-themed mementos.