For decades, tens of thousands of West Coast monarch butterflies (Danus plixippus) have overwintered at Natural Bridges State Beach in Santa Cruz, California. From October through March, in the park’s wind-protected grove of eucalyptus trees, the monarchs rest from their long migration. Thick clusters of monarchs intertwine their legs and hang from the branches like orange leaves, except that these leaves take flight when the temperature rises above 55 degrees Fahrenheit.
Monarchs are the only butterfly species that takes multiple generations to complete one round-trip migration. They travel 50–100 miles a day to escape the cold, and the round trip requires 4–5 generations to complete. A single generation can make the ~3,000 mile trip south, but the journey back north takes 3–4 generations to complete.
Monarchs that live east of the Northern Rockies overwinter in the Sierra Madre mountain range of Mexico, and those west of the Northern Rockies overwinter along the California coast. The butterflies return to the same groves each year for much-needed rest and to lay their eggs on nearby milkweed, which is the only plant that their larvae can eat.
Monarch populations everywhere have significantly decreased. In Santa Cruz, the population has dropped from a high of 150,000 to just a few thousand butterflies. Both Roundup and deforestation are to blame. Illegal logging has shrunk the eastern butterflies’ winter habitat in Mexico, and the introduction of Roundup-ready corn and soybeans in the US has almost eliminated milkweed from much of their habitat. Fortunately, parks such as Natural Bridges are being actively managed to keep some monarch habitat intact.
A Monarch Refuge
Natural Bridges State Beach park rangers tend a milkweed garden for their winged visitors so the butterflies have a place to lay their eggs. They also maintain adequate shelter for the adult monarchs. Since a fungal disease called pitch canker killed some of the Monterey pines that protected the monarch’s eucalyptus grove from the wind, they have been planting cypress trees in the park as a replacement wind break.
Docents lead tours of the Monarch Grove at Natural Bridges from mid-October through January at 11 AM and 2 PM on weekends. Tours start at the Visitor Center. The park also holds a Welcome Back Monarchs Day on the second Sunday in October and a Migration Festival on the second Saturday in February for the beloved butterflies.
Even with lower numbers than in the past, it is still spellbinding to stand in the quiet eucalyptus grove at Natural Bridges and see the orange clusters of monarchs weighing down the branches. As the temperature warms and the butterflies begin to gently flit around the grove in search of food, their delicate wings glow in the sun like stained glass. The only sound is the creaking of eucalyptus branches, the click of cameras, and hushed murmurs of awe as visitors witness one of nature’s most beautiful phenomena.
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This piece is part of the Santa Cruz Marine Protected Areas Beaches Tour made possible by the Santa Cruz Collaborative with support from the California Marine Sanctuary Foundation and the Resources Legacy Fund. Download the free app with many tours of the Santa Cruz area and beyond.
- Natural Bridges State Beach. California State Parks website.
- Migration and Overwintering. USDA Forest Service website.
- Personal communication with Martha Nitzberg, California State Park Interpretive Ranger, Natural Bridges State Beach, April 2016.
- Tracking the Causes of Sharp Decline of the Monarch Butterfly, by Richard Conniff. Yale Environment 360 website, April 1, 2013.