California Monarch Butterfly Population Experiences Steep Decline
Monarch butterflies in California face critical threats as populations plummet to near-record lows due to climate change, habitat loss, and more.
The iconic black-and-orange Western monarch butterfly, long cherished across California, is now facing one of the most severe population crises in its recorded history. Recent surveys have shown that their numbers have dropped dramatically in a single year, sparking urgent calls from scientists and conservationists for immediate action to avert potential extinction.
Understanding the Monarch Butterfly Decline
Monarch butterflies in California historically painted spectacular scenes each winter as they clustered by the millions in tree groves along the state’s coast. Today, their overwintering populations have plummeted by over 95% compared to the numbers recorded in the 1980s. The annual Western Monarch Count, a citizen science initiative led by the Xerces Society for Invertebrate Conservation, tracked just 9,119 monarchs overwintering in California this season—marking the second-lowest population since surveys began in 1997 . This follows three consecutive years where totals had rebounded above 200,000, but remains well below historic counts in the millions.
- Peak population (1980s): Up to 4 million monarchs annually
- 2020 low: Fewer than 2,000 monarchs
- 2024 count: 9,119 monarchs—a 96% drop from the previous year’s 233,394
This dramatic crash in numbers is stoking fears among experts: There is now an estimated 99% chance that the Western monarch population could become functionally extinct by 2080 without significant intervention.
Why the Western Monarchs Are Disappearing
The reasons behind this catastrophic decline are complex and interwoven, with each contributing to a challenging environment for monarch survival:
- Habitat Destruction: Urban development and agricultural expansion have destroyed native milkweed and nectar plants needed by monarchs for breeding and feeding .
- Pesticide Use: Widespread application of herbicides and insecticides reduces milkweed and poisons butterflies directly .
- Climate Change: Increasingly unpredictable and extreme weather patterns—such as prolonged droughts and heatwaves—compromise monarch reproductive cycles and migration success .
- Wildfires: Fires in places like Topanga Canyon have destroyed critical overwintering sites, compounding the pressures on remaining populations .
- Disease and Parasites: Disease outbreaks further weaken already vulnerable populations.
According to field biologists, unusually hot and dry fall conditions in 2024 slowed monarch breeding and delayed the transformation of caterpillars to butterflies, further reducing the number of butterflies that reached overwintering sites . Local wildfires also eliminated key groves that hosted hundreds to thousands of monarchs in previous years, exemplifying how sensitive these insects are to sudden environmental change.
Snapshot: Monarch Butterfly Population by the Numbers
| Year | Estimated Monarchs Observed in California |
|---|---|
| 1980s | 2–4 million |
| 2020 | <2,000 |
| 2023 | 233,394 |
| 2024 | 9,119 |
These numbers highlight why conservationists regard the 2024 overwintering season as dire and a clear wake-up call for those invested in monarch and pollinator survival .
Where Monarchs Congregate: Key Overwintering Sites in California
Every winter, volunteer community scientists, working in partnership with the Xerces Society and other organizations, count monarchs at hundreds of known overwintering sites from the northern to southern California coast. This coordinated effort, called the Western Monarch Count, covers:
- 257 monitored sites along the California coast and Baja California, Mexico
- More than 400 volunteers
What others are reading
The 2024 survey revealed that monarchs showed up in considerably fewer numbers at even the most well-known sites. For example:
- Lighthouse Field State Park (Santa Cruz): 1,406 monarchs counted
- Natural Bridges State Park (Santa Cruz): 1,400
- Moran Lake (Santa Cruz): 645
- Pismo Beach Monarch Butterfly Grove (San Luis Obispo): 556
- Skywest Golf Course (Hayward): 477
Some sites that historically hosted tens of thousands of monarchs saw numbers drop to the hundreds or, in some tragic cases, near zero after nearby wildfires or habitat destruction. For example, Lower Topanga Canyon, which recorded over 100 monarchs the previous year, counted virtually none in 2024 following significant fire damage .
What About the Eastern Monarch Butterfly?
Monarchs in North America are grouped into two distinct populations:
- Western population (overwinters in California, migrates across the western states)
- Eastern population (overwinters in the mountains of central Mexico, summers in the central and eastern United States)
Interestingly, while the Western population suffered a historic low in 2024, the Eastern monarch butterfly population actually saw an unexpected rebound. This winter, the Eastern population occupied about 4.4 acres at their overwintering sites in Mexico—double the area compared to the previous year. However, experts warn that this should not be mistaken for a recovery, as the Eastern population has still fallen by 80% over the last three decades and remains imperiled .
Factors Influencing Monarch Butterfly Populations
It is important to distinguish between natural year-to-year population fluctuations—due to weather patterns, food availability, and predators—and the current human-driven pollinator crisis threatening the monarch’s long-term survival. While butterfly numbers do vary each year, dramatic and sustained declines across multiple decades signal a systemic problem .
- Climate fluctuations (heat, drought, untimely storms) disrupt migratory cues and availability of host plants.
- Pesticides and herbicides directly poison monarchs and indirectly eliminate their sole larval food source: native milkweed.
- Loss of milkweed and wildflower habitat due to land-use change leaves monarchs unable to lay eggs or feed en route.
- Wildfire and disease add stress, reducing reproductive success and prompting local extirpations.
- Habitat fragmentation isolates remaining populations, making recovery more difficult.
Conservation Efforts and Urgent Calls for Action
The severity of the monarch butterfly crisis has prompted strong calls for both grassroots and policy-based interventions. Several key strategies are now widely promoted by experts and conservation organizations:
- Protect and restore overwintering habitats: Efforts to conserve and rehabilitate California’s eucalyptus and native tree groves are crucial for successful monarch wintering.
- Increase availability of native milkweed: Native milkweed is the only plant monarch caterpillars can eat. Expanding milkweed corridors along migration routes provides essential breeding habitat.
- Reduce pesticide use: Managing agricultural and residential chemicals is vital for pollinator safety.
- Promote pollinator-friendly landscaping: Encourage public and private landowners to incorporate native plants, including fall-blooming flowers, which offer nectar late into the migratory season.
- Advocate for legal protections: Listing the monarch butterfly as an endangered species on federal and state lists would unlock critical resources for their recovery.
- Public participation in citizen science: Monitoring and reporting sightings via programs like the Western Monarch Count helps researchers track trends and assess recovery efforts .
How Californians and Others Can Help
Everyone has a role to play in saving monarchs. Here’s what individuals, communities, and policymakers are urged to do:
- Plant native milkweed and nectar flowers in home gardens, schools, and public spaces.
- Avoid pesticide application during monarch breeding and migratory periods.
- Preserve existing monarch overwintering sites by supporting local conservation projects.
- Observe and report monarch sightings to community science databases, especially during migration and winter clusters.
- Educate others about the monarch decline and advocate for pollinator protection policies in local government.
- Support organizations like the Xerces Society, California State Parks Foundation, and local wildlife groups.
As California celebrates biodiversity and calls for stewardship, the monarch serves as both a warning and a beacon, highlighting the essential role of healthy ecosystems and engaged communities in reversing the decline of one of North America’s most celebrated insects.
Frequently Asked Questions (FAQs)
Q: Why are Western monarch butterfly populations declining so rapidly?
A combination of habitat destruction, pesticide use, climate change, disease, and wildfires has created a perfect storm of threats, making it difficult for populations to recover naturally.
Q: Are Eastern monarch butterflies facing the same crisis?
While the Eastern monarchs experienced an increase in their population this year, overall numbers have declined steeply over the past decades, putting them at ongoing risk of extinction.
Q: What is being done to protect monarch butterflies in California?
Conservation organizations and agencies are working to restore overwintering habitats, increase milkweed planting, reduce pesticide use, and promote legal protections. Public participation in monitoring and advocacy also plays a critical role.
Q: How can ordinary citizens help monarch butterflies?
Individuals are encouraged to plant native milkweed, avoid harmful pesticides, support conservation programs, and report monarch sightings to help scientists track population trends.
Q: What does the future hold for the monarch butterfly if current trends continue?
If threats continue unchecked, scientists estimate there is a 98–99% probability that the Western monarch population will face extinction within the next 60 years.
California’s monarch butterflies stand at a crossroads, a symbol of both fragility and resilience. Whether this remarkable species survives for future generations will depend on swift, collaborative action from all levels of society.
References
- https://www.latimes.com/california/story/2025-01-31/california-monarch-butterfly-population-hits-alarming-low-fire-wipes-out-topanga-habitat
- https://www.kqed.org/science/1995508/monarch-butterflies-are-on-the-decline-in-california-heres-why
- https://blog.nwf.org/2025/03/making-sense-of-butterfly-declines/
- https://www.calparks.org/press/californians-urged-observe-and-report-monarch-butterfly-sightings
- https://www.xerces.org/press/western-monarch-butterfly-population-declines-to-near-record-low
- https://monarchjointventure.org/blog/western-monarch-population-continues-to-decline
- https://wildlife.ca.gov/Conservation/Invertebrates/Monarch-Butterfly
- https://calmatters.org/newsletter/monarch-butterfly-count/
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