February 1, 2023

Local monarch butterfly population looking up for the second year

Preliminary population count reports 129,000 butterflies in San Luis Obispo County, up from over 90,000 in 2021

– The annual western monarch butterfly count by the Xerces Society for Invertebrate Conservation is reporting a dramatic increase in the local population of the iconic orange and black western monarch butterfly for the second year in a row. This year’s preliminary population count reports 129,000 butterflies in San Luis Obispo County, up from over 90,000 in 2021. So far, the total for the first 2022 western monarch butterfly count for California reports more than 300,000 increasing from 247,237 in 2021.

The Xerxes Society conducts two annual population counts at the monarch overwintering sites. The first count for 2022, known as the Thanksgiving Count took place between Nov 12 and Dec 4. The New Year’s Count will take place between Dec 24, 2022, and Jan 8, 2023. The largest populations of overwintering western monarchs are found in California with the densest populations this year at locations in San Luis Obispo, Santa Barbara, and Ventura counties. The society will issue a final report in late Jan 2023 after all the data have been compiled.

Scientists began reporting declines in the western monarch population in the 1990s. The local SLO County populations reported during the past two years are the highest since 1998 when 182,000 butterflies were counted. Even though the past two years are a significant rebound from only 2000 butterflies counted in 2020 for the entire state, the western monarch still has a struggle ahead to reach the millions that used cluster on branches at overwintering sites and flutter through backyards and fields on their annual breeding migration.

In 2014 the Xerxes Society petitioned the U.S. Fish and Wildlife Service to list monarchs on the federal Endangered Species List. That petition is still under consideration. The California Department of Fish and Wildlife designated the monarch as imperiled and vulnerable, protecting the butterfly from being removed from the wild, except with a permit for scientific studies and propagation. In July 2022, the International Union for Conservation of Nature (IUCN) added the monarch to the IUCN Red List of Threatened Species, giving the butterfly endangered status. The IUCN reports that climate change and habitat destruction are major contributors to population decline.

Habitat creation and restoration by gardeners, California native plant enthusiasts, and programs spearheaded by the Xerxes Society and other conservation groups seem to be helping. Pollinator gardens are an important food source for all pollinators including the monarch. Before rushing out and buying butterfly-attracting plants, know there are some differences between the western monarch, which migrates and overwinters west of the Rocky Mountains and the eastern monarch, which migrates east of the Rocky Mountains and overwinters in Mexico.

Both the western and eastern monarchs lay their eggs on milkweed, but the type of milkweed is important. The monarch caterpillar feeds on milkweed and the wrong milkweed can be a health threat. Plant milkweed that is native to the region at least five miles inland from the overwintering sites to encourage migration. Pollinator gardens and natural landscapes full of nectar-rich flowering plants and native California milkweed will feed the monarchs and attract them to lay their eggs.

monarch butterfly population increases

The western monarchs leave their overwintering sites when the weather begins to warm in the spring and begin breeding and migrating north as far as British Columbia, returning to the overwintering sites in the late fall. Plants that flower from spring through fall provide food, and milkweed native to the environments provide places for the female to lay eggs.

The butterflies that leave the overwintering site to head north are not the same ones that return. The western monarchs that head north only live about 5 weeks during which time they mature, breed, and lay eggs over three generations. The fourth generation is the longest-lived, flying back to the overwintering site in the fall and starting the northern migration in the spring.

Locally, overwintering sites that are open to the public include the Pismo Beach Monarch Butterfly Grove, the Morro Bay Golf Course, and the Fiscalini Ranch Preserve. There are also dozens of private properties in the local area and the Xerces Society reports that private sites are added every year.

For more information about the western monarch butterfly and creating or restoring habitats visit: