Update on the Monarch Butterflies at the Pacific Grove Sanctuary

This post was authored by Clemencia Macias

State of affairs

The Monarch Butterfly migration to the PG Sanctuary from October 2020 to March 2021 has been a total catastrophe. Unfortunately, no Monarchs clustered and overwintered at our dear Sanctuary.  Only a few monarchs were spotted in the Sanctuary, a few days only, in the low single digits, during the months of October through December.

The reasons are still being pondered by the Sanctuary caretakers, general citizens, City personnel and scientists. Climate change has affected the butterfly population.

Most of the overwinter sites in Coastal California, San Luis Obispo, Monterey and Santa Cruz counties, have experienced tremendous declines in the number of Monarchs that arrived this year.  As of January 2021, the total count(1) of Monarch Butterflies in key sites in those counties was:

Monarch Grove Sanctuary, Pacific Grove = 0 (down from 47,000 in 1997)

Natural Bridges State Beach – CA State Park, Santa Cruz = 550 (down from 120,000 in 1997)

Pismo State Beach- CA State Park, Pismo Beach = 199 (down from 100,000 in 1997)

What is happening?

Theories about the low numbers this year include the California fires that took place all over the Northern part of the State and agricultural pesticides used in their migratory path.  The fires rage destroyed much of the forests, bushes and flowers; habitat needed by the butterflies to rest and obtain the nectar to continue their trip down South. Thus, fires have jeopardized their ability to survive and arrive at the overwinter sites.

Also, the microclimate condition of the Sanctuary has changed dramatically. We have monitored stronger winds coming from the South and West boundaries. The branches where the Monarchs used to cluster, in eucalyptus, Monterey pines or cypresses, have disappeared due to cutting and trimming during the last 10 years. Management actions had major impacts on clustering. We are working on restoring those tress and branches to break the winds and recreate the appropriate conditions for clustering, mating and overall winter survival.

The Monarch numbers are plummeted, and they are in peril. The long-term decline could be attributed to habitat loss and degradation, increase pesticide use and the effects of climate change.

What can you do?

Plant flora that bloom anywhere between  October to February. This provides much needed nectar to the monarchs. Planting native nectar bushes and trees that have not been treated with pesticides can help.

Planting milkweed in the coastal areas is not recommended. Instead, plant flowers for nectar support. The natural pattern of the Monarchs in California is to mate around February, when the female migrates to the Central Valley and will lay her eggs on the milkweed leaves. The caterpillar would ONLY eat milkweed, until it is ready to form into a chrysalis!

We discourage home butterfly growing or releasing butterflies in any of the overwinter sites. They tend to be lost, they don’t moved ( or stay still, without fluttering) or not survive. This butterfly suddenly is placed in an unknown environment in contrast to wild monarchs that flew thousands of miles to get there.

Spread the word to friends and family! Thank you for visiting the Pacific Grove Monarch Sanctuary, a critical overwinter site!


  1. The Xerces Society, Western Monarch Thanksgiving Count 1997-2020



Links for more info:

  1. https://www.westernmonarchcount.org/data/


  1. https://baynature.org/2020/12/04/with-fewer-than-2000-butterflies-counted-western-monarch-takes-an-astonishing-step-closer-to-extinction/


  1. https://xerces.org/blog/western-monarch-population-closer-to-extinction-as-wait-continues-for-monarchs-protection