Monarch butterflies face steep decline in the Western U.S.

Monarch butterflies have long symbolized transformation and resilience. Their fragile yet determined migration across North America has captivated scientists and nature enthusiasts.

Each year, these vibrant orange-and-black-winged insects embark on a remarkable journey, covering thousands of miles to reach their wintering grounds. However, recent findings paint a troubling picture.

The number of western monarch butterflies has fallen to its second-lowest count in nearly 30 years. A combination of habitat destruction, pesticide exposure, and climate change threatens the survival of this iconic species.

Conservationists and researchers are scrambling to understand the reasons behind this sharp decline and what can be done to protect these beloved pollinators.

Monarch butterfly surveys

For decades, scientists have monitored monarch populations to track changes in their numbers. Monarchs found in the eastern United States migrate south to Mexico, where they are counted each year by researchers from the World Wildlife Fund.

However, monarchs west of the Rocky Mountains follow a different path and overwinter along the California coast.

Since 1997, the Xerces Society for Invertebrate Conservation has conducted annual counts of western monarchs. These surveys cover multiple locations, including coastal California, northern Baja California, and inland regions of California and Arizona.

In 1997, researchers recorded the highest-ever population numbers – a total of 1.2 million butterflies. That number has plummeted over the subsequent years, reaching a devastating low of just 1,901 monarchs in 2020.

Despite a brief resurgence in recent years, the latest survey results are alarming. In 2024, only 9,119 monarchs were counted – a staggering 96 percent drop from the 233,394 recorded in 2023. This marks the second-lowest population count since the survey began.

Decline in key wintering sites

One of the most dramatic declines was observed at a key wintering site owned by The Nature Conservancy in Santa Barbara.

This location hosted 33,200 monarchs last winter. In 2024, the number fell to just 198. Such steep declines raise concerns about the future stability of monarch populations in the region.

While the reasons for this sudden decrease are not entirely clear, experts point to several contributing factors. Loss of milkweed, the primary host plant for monarch caterpillars, remains one of the biggest challenges.

The plant’s habitat has been shrinking due to agricultural expansion, urban development, and prolonged droughts. Pesticides also play a major role, contaminating milkweed and poisoning caterpillars before they can mature into butterflies.

Extreme heat and monarch butterflies

Weather conditions also significantly impact monarch populations. While habitat destruction and pesticide exposure remain persistent threats, extreme heat waves may have played a crucial role in this year’s decline.

According to Emma Pelton, an endangered species biologist with the Xerces Society, monarchs struggle when temperatures reach 100 degrees Fahrenheit (37.7 Celsius). Prolonged exposure to temperatures above 108 degrees Fahrenheit (42.2 degrees Celsius) can be fatal.

“The monarch population is already small,” Pelton said. “Triple-digit heat in the western states last year may have slowed breeding.”

The summer of 2023 saw multiple heat waves across the western United States. In July, Palm Springs set a record high of 124 degrees Fahrenheit (51.1 degrees Celsius).

A second wave of extreme heat hit northern California in early October, with multiple cities breaking temperature records. These conditions may have reduced breeding success and weakened the already vulnerable monarch population.

History of dramatic population swings

Although the 2024 population decline is severe, western monarchs have demonstrated an ability to recover in the past. In 2020, when the population hit its all-time low of 1,901 individuals, many feared the species was on the brink of collapse.

Yet, the following year their numbers soared to 247,246 – an increase of nearly 13,000 percent. The upward trend continued in 2022, with the survey recording 335,479 monarchs.

“This is bad news,” Pelton said. “But we have seen incredible recovery. This doesn’t mean we’re not going to have western monarchs. It’s hopefully a wake-up call that a bad year can set them back pretty significantly.”

The rapid rise and fall of monarch populations suggest that they have the potential for quick recovery, provided conditions improve. However, conservationists warn that without sustained efforts to protect their habitat and food sources, monarchs may struggle to bounce back in the future.

Federal efforts to protect monarch butterflies

In response to the ongoing decline, the U.S. Fish and Wildlife Service announced in December 2024 that it is taking steps to list monarchs as a threatened species.

If granted, this status would provide crucial legal protections. Killing or transporting monarchs, or destroying monarch habitats would be prohibited under federal law.

The proposal also includes protections for 4,395 acres of land across seven coastal California counties. These areas serve as essential overwintering sites for western monarchs.

If the listing is approved, conservationists hope it will slow habitat destruction and create safer breeding grounds for monarch populations to recover.

A public comment period on the proposal remains open until March, allowing experts and the public to weigh in on the decision. Officials have until December 2025 to finalize the listing.

Calls for stronger pesticide regulations

Beyond habitat loss, pesticides pose a major threat to monarchs and other pollinators. In December 2024, the environmental law firm Earthjustice petitioned the Environmental Protection Agency to strengthen pesticide regulations.

Their request focused on requiring companies to assess how their products affect insects such as bees, moths, and butterflies.

While some pesticides have been linked to monarch declines, many remain widely used in agriculture. Conservation groups argue that without stricter oversight, pesticide exposure will continue to harm pollinators and reduce their chances of survival.

The fate of monarch butterflies

The future of western monarchs remains uncertain. Conservationists stress that efforts to restore milkweed habitats, protect overwintering sites, and regulate harmful pesticides must continue.

While federal protections may provide some relief, long-term recovery will require a collective effort from governments, researchers, and the public.

For now, the sight of monarch butterflies filling the skies each year remains in jeopardy. The next few years will determine whether these iconic pollinators can withstand the mounting pressures against them or if they will fade into memory as another casualty of a changing world.

Information in this article was obtained from an online press release.

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