Western monarchs fell from millions to under 2,000: what the Park Service and you can do

Western monarchs once wintered on the California coast in the millions, but in the 2020-2021 overwintering period fewer than 2,000 were counted. The National Park Service (NPS) says the butterflies are more than beautiful: as they feed from flower to flower they pollinate many wildflowers, choosing bright, clustered flowers that stay open by day and offer flat landing pads. One plant, though, is essential: milkweed.

Monarch butterflies need milkweed to survive. Photo: NPS.

Why they are declining

Female monarchs lay eggs only on certain milkweeds, on the underside of the leaves, and the caterpillars that hatch feed on the plant as they grow. Milkweed is often eradicated as a noxious weed, and urbanization, large-scale industrial farms and drought have cut its numbers too. Together with the loss of winter habitat in California and Mexico, pesticides and climate change, that contributes to the decline of western monarchs.

Monarchs lay eggs under milkweed leaves, and the caterpillars feed on the plant. Photo: NPS / M. Reed.

In the 1990s it was common to see 3 to 10 million butterflies migrate to overwintering sites along the California coast. In the count for the 2020-2021 overwintering period, fewer than 2,000 western monarchs turned up, which alarmed scientists and butterfly enthusiasts. The next count was better, with 250,000 in the core area of central California from Monterey to Los Angeles counties, though the rise was not seen everywhere, and numbers in the San Francisco Bay Area stayed low.

What NPS and partners do

With partners and community scientists, NPS plants milkweed, holds pollinator festivals, monitors monarchs, does research and restores habitat. Staff help with butterfly counts, support a community science program that maps western milkweed, and take part in International Monarch Bioblitzes. In the San Francisco Bay Area, community science monitoring coordinated by NPS staff records monarch overwintering at San Francisco and coastal Marin NPS sites. It tracks population trends and involves partners including the Xerces Society and the Monarch Joint Venture.

In 2021 Golden Gate National Recreation Area, using grant funding, began working with OneTam on site assessments and implementation plans, an inventory of wild milkweed stands, and outreach and education for young people, stakeholders and the Bay Area community. Staff are also working with their cooperating associations on pop-up programs, webinars, locally made artwork and monitoring at other former historic sites. NPS considers this focus critical because northern overwintering sites may be increasingly favored under future climate predictions, and they are the first step before monarchs move to their breeding areas.

How you can help

Help monarchs in your own backyard. Photo: NPS.

• Plant milkweed and other nectar plants. Native flowering plants can make a waystation for monarchs, and the Monarch Joint Venture has planting guides.
• Be a community scientist. Photograph western monarchs and milkweed and upload them to the Western Monarch Mapper, or use iNaturalist wherever you live.
• Limit pesticides. Before spraying, ask whether flowers are in bloom or pollinators are active, whether there is an alternative, and whether you are following the instructions. Pollinators can be harmed by nectar or pollen that has touched pesticides, and applying them at night, when butterflies are inactive, reduces exposure.
• Buy organic and buy local. Organic crops use fewer pesticides, and buying local cuts carbon emissions and supports farmers who provide pollinator habitat.
• Pass it on. Tell others why native plants support pollinators such as monarchs.

Sources

• National Park Service, article "Protecting Western Monarchs", for Golden Gate National Recreation Area: https://www.nps.gov/articles/000/protecting-western-monarchs.htm. Photographs credited to non-NPS photographers or naming staff members are left out; rewritten in hubnx's own words.