1000% Increase in Overwintering Monarch Population along Central Coast California as of Jan. 2022!

 

What a difference a year makes. In November 2020, the overwintering count was so low (less than 2,000 across approximately 4000 sites in central coast California) that it was dubbed the ‘collapse of migration’. This past November 2021 the count, verified at the New Year’s count, revealed 250,000 monarchs!
An astounding rebound in just one year.
 

What was responsible for this amazing rebound is not known! Monarch butterflies are resilient and adaptable, but conservation scientists have done calculations, and 2,000 overwintering monarchs from Nov. 2020 cannot propagate sufficiently to product 250,000 monarchs in Nov. 2021. Was it the large increase in winter propagation in the Bay Area and southern California, referred to as resident monarchs this past year? Are there monarch populations in areas across the western states no one is aware of? These question and more are on the minds of conservation scientists as more and more research is being done to understand where and when monarchs are breeding and migrating in California.

 

Monarch butterflies that breed in North America west of the Rocky Mountains are known as western monarchs. In the late fall, most western monarchs have migrated to the California coast and spent the winter (late November to February) clustering in groves of pine, cypress, and eucalyptus trees, during which time they do not breed (reproductive diapause). As temperatures warm and daylight hours increase in February, they mate and migrate inland to lay eggs on emerging milkweeds.

 

Historical Migration Perspective:

According to Xerces, 4.5 million monarchs overwintered on the California coast in the 1980’s. By 1997, there were 1.2 million monarchs. As of 2015, that number had declined to 293,000; in 2019, the decline fell to 30,000 and, in 2020, less than 2,000. This was alarming to monarch conservationists and urban gardeners alike.

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In November 2020, there were also a significant number of monarchs found inland and in southern California that bred throughout the winter sustained by non-native tropical and balloon milkweed. That year there was a large “urban” or resident population. Reports of dozens of eggs being laid on mostly non-native milkweed all winter led to reports of hundreds of monarchs eclosing (emerging) from chrysalides January thru March 2021. Now, in 2022, we are happy to report the unprecedented increase to 250,000 overwintering monarchs. What population spread occurs from this population to all areas of California as well as other western states is eagerly awaited.

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What can Californians do to help?

Many Californians and conservation groups are asking, what can individuals do to help the monarch population sustain and grow to increase the recovery of the population of western monarchs, as 250,000 is still much lower than needed for long-term sustainability. Most critical is for as much monarch butterfly habitat be planted as possible and overwintering sites restored and developed. Native milkweed is the recommended by Xerces and California Department of Fish and Wildlife (CDFW) along with nectar plants. Non-native milkweed, especially tropical milkweed Asclepias curassavica, is still quite available and used by resident monarchs as well as overwintering monarchs that disperse to feed and breed in February, before native milkweeds have come back from dormancy. There is still controversy over the pros and cons of tropical milkweed with conservation scientists both pro and con.

 

On a positive note, March thru October of 2021 found a great deal more native milkweed available through growers and nurseries throughout California. Other organizations, such as Monarch Watch and Xerces, provided plugs of native milkweed free to 1 acre or larger habitat restorations as well as for purchase at smaller quantities. In addition, Regional Conservation Districts, funded by the State of California developed restoration projects for overwintering sites and began research on  early growth native milkweeds that might be available in February when overwintering monarchs disperse to feed and breed. Many non-profits and local monarch enthusiast also initiated planting many small new butterfly gardens across California and provided more educational programs for the public. As a result, the April thru October 2021 monarch propagation in California was substantial.

Another significant change in 2021 was the effort by conservation groups, Facebook groups, blogs, and websites to educate the public about the California Department of Fish and Wildlife Ruling that declared ‘no touching and no rearing’ of monarchs allowed in California. The reason for the Ruling is to allow Nature to proceed untampered with by humans. This is standard in conservation efforts. With monarchs, it intended to eliminate urban gardeners from protecting caterpillars and chrysalids; no putting them into habitats or raising eggs, caterpillars or chrysalids inside; and no mass rearing. This was, of course, a major change for many urban gardeners who have long felt compelled to save every egg and caterpillar possible. However, in conservation science, this activity promotes saving weak or even sick caterpillars, and weakens the overall population.

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Pesticides and Herbicides:

Of on-going critical importance for the survival of California monarchs as well as all pollinators is the reduction of pesticides and herbicides across all ecosystems. Gardeners are encouraged to eliminate pesticide use. Many monarch caterpillars are killed or weakened by ingesting plants that have been grown with pesticides or in gardens where they’re used. Neonicotinoids used by growers to bring plants to large retail stores are serious killers of pollinators from bees to butterflies. (Pesticides | The Monarch Joint Venture). The weed killing herbicide glyphosate (key ingredient in RoundUp and other herbicides) is another known toxin for milkweeds. Please participate in responsible pesticide use in our environment. Learn more from Pesticide Action Network (PAN) Pesticide Info | California Pesticide Use

 

Stay tuned for updates and recommendations for monarch butterfly gardeners and habitat creation across California. For more information on California monarchs by region, see below.