How Did the Western Monarchs Do This Winter in California?

In April I visited Pismo State Beach's Monarch Butterfly Grove. I knew there wouldn't be any western monarchs who overwintered remaining there (though I saw three flying around!), since they left a few weeks prior to begin their annual migration north. But I was curious: How did California's shrinking monarch population do this winter? The short answer is they did relatively well. . .but before getting to the details, let's review their current status.

Monarchs in Trouble

The colorful orange-and-black, magnificent monarch butterflies (Danaus plexippus) are the world's most recognized and beloved butterflies.  Yet, they are increasingly in danger of becoming extinct. An announcement last summer from International Union for Conservation of Nature (IUCN) announced the monarch butterfly had been put on its "Red List of Threatened Species as Endangered” due to habitat destruction, climate change, and pesticides, with the primary reason being reduction in milkweed plants that are so vital to their survival.

IUCN stated: "The western population is at greatest risk of extinction, having declined by an estimated 99.9%, from as many as 10 million to 1,914 butterflies between the 1980s and 2021.” In addition, "The larger eastern population also shrunk by 84% from 1996 to 2014. Concern remains as to whether enough butterflies survive to maintain the populations and prevent extinction."

This Year's Status

According to a recent article by Tara Duggan (https://www.pressreader.com/usa/san-francisco-chronicle-late-edition/20230201/281595244675872) the 2022 annual Thanksgiving count organized by Xerces Society showed relatively high numbers of western monarchs this year with over 330,000 found in overwintering sites throughout California's central coast. This is a significant increase from the winter of 2020-21 when fewer than 2,000 were counted and they were thought to be on the threshold of extinction. The 2021-2022 count the following year was much better, at 250,000.

At the Pismo Beach monarch sanctuary, a board showed some of the tallies made over the years:

1990 – 230,000

1995 – 150,000

2000 – 40,000

2005 – 32,000

2010 – 24,000

2015 – 28,000

2017 – 12,300

2019 – 6,000

2020 – 188

2021 – 22,700

2022 – 24,128

The same board also showed the 2022-2023 Pismo Beach sanctuary monarch migration season count (October-February) from their peak numbers after arriving from the north in autumn to their departure in mid-February for the beginning of their annual northward migration. Presumably the decreasing numbers between November and December was due to winter storms.

11/15/22 – 24,100

11/30/22 – 19,177

12/13/22 – 15,707

1/17/23 – 15,817

2/7/23 – 15,015

2/21/23 – 4,628

How You Can Help

• Plant nectar plants for the adults!  While caterpillars feed only on milkweed, the adult monarch feeds on nectar from flowers while migrating. Native plants with tubular or funnel shapes are particularly attractive and nutritious for all butterflies.
• Plant milkweed! This plant is crucial to monarchs' survival since it is the only plant females lay their eggs on and the only source of food for the emerging larvae. When possible, plant from seed. If you purchase plants ask the nursery or garden center if the grower treated the plants with pesticides. The best time to plant is in the fall months when it's cooler, at the start of the rainy season. Local native milkweed varieties include:

o   Asclepias fascicularis (Narrowleaf milkweed)

o   Asclepias speciosa (Showy milkweed)

o   Asclepias syriaca (Common milkweed)

o   Asclepias cordifolia (Heartleaf milkweed)

 

• Use UC Integrated Pest Management as a resource: (https://ipm.ucanr.edu/PMG/menu.homegarden.html). If you use a pesticide, avoid broad spectrum pesticides, selecting a pesticide for the specific pest/disease, or choose one that is less toxic such as horticultural oils and insecticidal soaps. Be sure to follow instructions and apply in early morning or late evening when pollinators are unlikely to be present.
• Get involved in the annual western monarch Thanksgiving and New Year counts (https://www.westernmonarchcount.org/) and/or tagging monarchs to monitor their migration patterns (https://www.monarchwatch.org/tagging/)

 

What Will the Future Bring for the Western Monarch?

This winter season's higher annual count numbers, while encouraging, are far below the historical counts, in the millions, of the 1980s. These beloved graceful creatures still have many challenges ahead. However, California state has invested over $1 million in monarch habitat restoration, including planting more milkweed, particularly here in the Central Valley, which is a part of their migratory flight path.

Only time will tell if their numbers will increase, but scientists say these efforts could help the western monarch population recover. By planting milkweed and native flowering plants in our gardens, we can be a part of this ongoing endeavor and hopefully be able to see more of these magnificent butterflies floating about in our gardens in the future.

To learn more about the life cycle and migration of the western monarch, read my article “Marvelous Monarchs” at https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=55249

 

Denise Godbout-Avant has been a UCCE Master Gardener with Stanislaus County since 2020