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Concerning Decline in California’s Monarch Butterfly Population
The population of monarch butterflies in the western United States has sharply decreased, with fewer than 10,000 individuals observed in California this winter. This drop raises serious concerns about the future of this iconic species.
An official count documented only 9,119 butterflies this season, as reported by the Xerces Society for Invertebrate Conservation. This figure represents the second-lowest total since monitoring began in 1997, following a stark low of under 2,000 monarchs recorded in 2020.
These figures highlight the critical nature of the U.S. Fish and Wildlife Service’s recent proposal to categorize the monarch as a federally endangered species. Data indicates that the western monarch population has decreased by over 95% since the 1980s, when estimates suggested a winter population of approximately 4 million butterflies in California, as per the California Department of Fish and Wildlife. Without significant conservation efforts, projections suggest a 99% risk of extinction for the western monarch by 2080.
Factors driving this decline include habitat loss, pesticide use, and extreme weather fluctuations exacerbated by climate change. This year’s particularly low count may further be linked to an unusually hot and dry fall, which likely disrupted butterfly breeding and slowed the transformation of caterpillars into butterflies, explained Emma Pelton, an endangered species biologist with the Xerces Society.
Additionally, local environmental stressors such as recent wildfires in the Los Angeles area have severely impacted the butterfly’s habitats. For instance, areas in Lower Topanga Canyon that previously harbored over 100 butterflies saw significant declines. A site in Santa Barbara County revealed a startling drop from 33,200 monarchs last year to just 198 this winter.
The annual count, conducted by approximately 400 volunteers across 257 sites in California and Baja California, Mexico, tracks the western monarch’s winter congregation before they migrate throughout the western states come spring. In contrast, the eastern monarch population, which has also declined by over 80% since the 1980s, migrates to central Mexico for the winter months.
This year’s count represents a sharp decline from the three preceding years, which saw populations exceeding 200,000 butterflies annually, largely due to favorable weather conditions. Despite these higher numbers, they reflect a troubling drop from the millions recorded in the 1980s, which scientists regard as a benchmark for a stable population.
“Insect populations typically fluctuate annually,” noted the California Department of Fish and Wildlife. “However, the overarching declining trend is alarming, particularly if existing threats are not addressed.”
The call for federally recognized protection for monarchs is not new; an initial petition was made in 2014, but it was tabled in light of other pressing conservation priorities. Recently, the U.S. Fish and Wildlife Service has renewed efforts to classify the butterfly as an endangered species.
“The monarch butterfly is a treasured species in North America, enchanting audiences of all ages with its remarkable life cycle. Despite its vulnerability, the monarch, like many elements of nature, demonstrates considerable resilience when afforded protection,” stated Martha Williams, the former director of the Fish and Wildlife Service.
To bolster conservation efforts, the Fish and Wildlife Service has proposed setting aside 4,395 acres in Alameda, Marin, Monterey, San Luis Obispo, Santa Barbara, Santa Cruz, and Ventura counties as critical habitat for the western monarch. They are currently accepting public commentary on this proposal and plan to reach a final decision by year-end.
Alongside these measures, the Xerces Society is advocating for the U.S. Environmental Protection Agency (EPA) to rigorously assess the impacts of pesticides on butterflies before allowing market approval. Current regulations primarily assess impacts on honeybees, neglecting other essential pollinators.
Research from the Xerces Society and the University of Nevada-Reno revealed that milkweed, the key food source for monarch caterpillars, is tainted with 64 different pesticides. Notably, methoxyfenozide was detected in 96% of milkweed samples, even though it remains permissible under existing regulations due to its low toxicity to bees.
“We understand that pesticides significantly contribute to declines in monarch and other pollinator species. Nevertheless, there are significant deficiencies in the EPA’s oversight, as most pesticides have never been evaluated for their impact on butterflies,” commented Rosemary Malfi, director of conservation policy at the Xerces Society. “How can we protect these invaluable species if we lack crucial data for informed decision-making?”
Source
phys.org