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Western monarch populations reach highest numbers in decades

  • The Western Monarch butterfly population has reached its highest number since the year 2000, with more than 335,000 butterflies counted during the annual Thanksgiving Western Monarch Count in California and Arizona.
  • Western monarchs winter in California and migrate thousands of miles each year, in a migration cycle that takes three to four generations. They are counted annually by volunteers at these sites.
  • The population rebound is a welcome development, but the species is still considered endangered and far from its population numbers in the 1980s, when millions of butterflies could be seen in the trees.
  • Conservation efforts include protecting wintering sites, planting native plants, reducing pesticide use, and supporting conservation initiatives; the public can also participate in community science projects and make simple changes to their gardens and communities.

The western monarch butterfly population hit its highest number since the year 2000, with more than 335,000 butterflies counted at their wintering sites in California and Arizona during the 26th annual Thanksgiving western monarch count.

“We can all celebrate this count,” Emma Pelton, a conservation biologist at the Xerces Society and leader of the Western Monarch, said in a news release. “A second consecutive year of relatively good numbers gives us hope that there is still time to act to save Western migration.”

More than 250 people took part in the 2022 Western Monarch Count, in which they surveyed sites along the California coast and a few others in interior California and Arizona in November and December. Volunteers counted groups of monarchs as they gathered to spend the winter in groves of trees, often made up of non-native eucalyptus species.

Monarch butterflies congregate in treetops for protection during the winter. Overwintering sites must provide particular combinations of protection from harsh weather, dappled sun and nectar. This cluster is located in Pacific Grove, California. Xerxes. Photo by Isis Howard / Xerces Society.

The largest gathering of butterflies, 34,180 individuals, took place on a private site in Santa Barbara County, California. Santa Barbara, Ventura and San Luis Obispo counties have sites that are home to more than 20,000 butterflies. The San Francisco Bay area has also seen a dramatic increase in recent years, with approximately 9,000 individuals found.

Some publicly accessible sites in California where the public can view the monarchs gathering include Pismo Butterfly Grove in San Luis Obispo County, Pacific Grove Sanctuary in Monterey County, and Natural Bridges in Santa Cruz County.

While this population rebounded from fewer than 2,000 counted in 2020 to over 335,000 in 2022 is welcome news, scientists estimate we are still more than 90% down from historical numbers in the 1980s and early 1990s. when millions of monarchs filled the wintering grounds in California.

“We know we still have a long way to go to achieve population recovery,” Pelton said, “and the storms that hit soon after mean we’ll start spring with much, much less than this total.”

Graph showing the size of the overwintering monarch butterfly population in California from 1997 to 2022 (green bars). The graph also shows the number of sites visited each year (blue line). Image from the Society of Xerces.

Scientists don’t know exactly why we’ve seen a rise in numbers over the past couple of years. But, Pelton said, butterfly numbers, like many other insect populations, fluctuate from year to year in response to temperature, rainfall and food availability.

The iconic monarch butterfly has been listed as endangered by the International Union for Conservation of Nature (IUCN), a global authority on the species’ conservation status. An endangered listing means that the species is likely to become extinct without significant intervention.

Monarchs meet the criteria to be listed under the US Endangered Species Act, which would ensure the protection of butterflies and their habitats, but the US Fish and Wildlife Service announced in December 2020 that the species would not be listed. listed, stating that other species are a higher priority.

“Unfortunately, there continues to be very little protection for the species or its habitat. Overwintering sites in particular continue to be destroyed and damaged every year,” said Isis Howard, conservation biologist at the Xerces Society and coordinator of the count.

A monarch butterfly (Danaus plexippus). Image by John Banks via Pexels (Public Domain).

Just after the Thanksgiving count ended, the California coast was hit by extremely intense rain events known as atmospheric rivers, resulting in flooding, falling limbs, and uprooted trees. Some wintering sites were unaffected, but volunteers from others reported an increase in the number of monarch butterflies that were lying on the ground and being blown off their clusters by severe weather, making them more susceptible to cold, wet conditions and predation.

“Small populations are especially vulnerable to being suffocated by extreme weather, so we’re lucky these storms occurred in a relatively good year,” Pelton said. “We don’t want to rely on luck alone to ensure the survival of the migration of Western monarchs.”

There are two populations of migratory monarch butterflies in North America, both famous for their impressive overland journeys extending up to 6,400 kilometers (4,000 miles). Eastern Monarchs spend the winter in Mexico, while Western Monarchs winter in California. In spring, all monarchs migrate north, some as far as Canada. This migratory cycle covers thousands of kilometers and takes three or four generations. Monarch population estimates are taken at these wintering grounds.

A map showing migration patterns of the monarch butterfly in North America. Monarchs winter along the California coast or in central Mexico (both areas are shown in red). From those areas they spread northward during the spring and summer to breed on milkweed, before the last generation of the summer travel to their wintering grounds. South Florida is colored purple to indicate that this is an area where monarchs do not migrate, but live year-round. Image courtesy of the Xerces Company.

Conservationists say we need to put more effort into protecting existing wintering sites and making them more resilient to the impacts of climate change. This can be achieved by replacing dead or dying trees, designing sites to prevent or reduce flooding, and growing native plants as nectar sources.

“The fact is, if we lose wintering sites in California, we could lose migratory western monarchs,” Howard said. “Development, eucalyptus removal and tree felling need to be managed carefully if we are to make room for these animals to survive.”

After leaving their wintering sites, western monarch butterflies depend on finding suitable habitat and protecting breeding grounds in multiple western states. Gardeners, park managers, schools, and others can play a role in the recovery of the western monarch population by making simple but effective changes, such as:

  • Cultivation of native milkweed plants (Asclepias).
  • Grow a variety of nectar plants, preferably native to your region.
  • Reduce or avoid the use of pesticides.
  • Encourage policymakers to support initiatives such as the Recovering America’s Wildlife Act and the Monarch Action, Recovery and Conservation of Habitat Act.
  • Participate in community science projects that monitor monarchs, such as the Western Monarch Milkweed Mapper, the Western Monarch Mystery Challenge, and the National Integrated Monarch Monitoring Program.
  • “So many people and organizations have come together to try and protect this butterfly and its habitats. From planting native milkweed and reducing pesticide use to supporting the protection of overwintering sites and contributing to community science, we all have a role to play in ensuring this iconic insect makes a full recovery,” said Anna Walker, a member of the IUCN Species Survival Commission Butterfly and Moth Specialist Group who led the IUCN Monarch Butterfly Assessment.

    “It’s hard to watch monarch butterflies and their extraordinary migration teeter on the brink of collapse,” she added, “but there are signs of hope.”

    Monarch caterpillars feed on milkweed plants. Photo by Bernard Spragg. New Zealand via Flickr. Public domain.

    Image of the flag of Monarchs Clustering on Monterey Pine in California. Photo courtesy of Photo courtesy of Carly Voight / Xerces Society.

    Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough

    Again from this reporter:

    Monarch butterflies are officially endangered

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