The iconic monarch butterfly (Danaus plexippus) meets the criteria to be listed under the U.S. Endangered Species Act — but will not be listed just yet because priority will be given to other species, the U.S. Fish and Wildlife Service (USFWS) announced Dec. 15.

This leaves the monarch as “a candidate species” for possible listing under the Endangered Species Act (ESA) in the future. As a candidate, its status will be reviewed each year until it is either added to the ESA or the populations recover.

“We in the Fish and Wildlife Service just concluded one of the most rigorous species status assessments ever conducted by our agency,” Charles Wooley, regional director for the USFWS in the Department of the Interior’s Great Lakes region, said in a press briefing. The species assessment, Wooley said, informed the USFWS decision that “listing the monarch is warranted but precluded at this time by higher priority listing actions.”

The “warranted-but-precluded” status is used by the USFWS when the service does not have enough resources, financial and/or human, to complete the process of listing a species because it must focus on other more vulnerable species or species involved in settlements due to litigation or court orders.

Currently, 161 other species are considered a higher priority than the monarch butterfly, including several freshwater snails and mussels, salamanders, frogs, snakes, crayfish, turtles, beetles, plants, birds, and the little brown bat.

Monarch butterflies on a branch in Michoacan, Mexico. (Photo by JHVEPhoto via Shutterstock, Mongabay)

There are two populations of monarch butterfly in North America: the eastern monarchs, which winter in Mexico, and the western monarchs, which winter in California.  All monarchs migrate north after the winter, sometimes as far as Canada. This journey, covering thousands of miles, takes three or four generations. Monarch population estimates are taken at their overwintering grounds.

Approximately 90% of monarchs belong to the eastern population, which has been declining for decades. The area inhabited by monarchs in their Mexican wintering grounds is used as a proxy for estimating the population size. Based on these area estimates, eastern monarchs numbered around 384 million in 1996 and fell to about 60 million in 2019.

The western monarch populations, which winter in California, have seen a more dramatic population decline, falling from about 1.2 million butterflies in 1997 to fewer than 30,000 in 2019. The Xerces Society, the group behind the annual count, says this number may be a tipping point for the species, below which the population may not recover.

This year’s Western Monarch Thanksgiving Count was “alarming,” according to the Xerces Society, with fewer than 2,000 individuals reported as of late November. The final count is expected to be less than 10,000, “the smallest overwintering population on record.”

“The U.S. Fish and Wildlife Service agrees that monarchs are threatened with extinction” Sarina Jepsen, director of endangered species at the Xerces Society, said in a statement. “However, this decision does not yet provide the protection that monarchs, and especially the western population, so desperately need to recover.”

The state of California recently determined it does not have the legal authority to protect insects under the California Endangered Species Act. The Federal Endangered Species Act can only include listings for species, subspecies or distinct population segments of vertebrates. Because monarchs are invertebrates, the western populations cannot be listed on their own at a federal level, leaving the western monarchs with limited avenues for protection.

Western monarch butterflies mating in Nevada. (Photo courtesy of Stephanie McKnight/Xerces Society, via Mongabay)

In 2014, the USFWS received a petition to list the monarch butterfly under the Endangered Species Act from the Center for Biological Diversity, the Center for Food Safety, the Xerces Society, and Lincoln Brower, the late emeritus professor of zoology at the University of Florida.

The USFWS began assessing the status of monarch populations in 2016 using “a rigorous analysis of the best available science,” Lori Nordstrom, USFWS assistant regional director for ecological services in the midwest region said in a press briefing. The final Species Status Assessment Report describes the influences on the future conditions of monarchs and projects future outcomes based on millions of simulations.

The largest influences on monarch populations, according to the USFWS status assessment, are the availability of milkweed and nectar sources, the availability and quality of winter habitat, exposure to insecticide, climate change (changes in weather and temperature), and conservation efforts.

Monarch health is affected by habitat loss and degradation from the conversion of grasslands to agriculture, herbicide and insecticide use, logging at overwintering sites in Mexico, urban development, and drought.

Under current conditions, the report says, the eastern monarch populations have about a 50%-70% chance of reaching a point at which extinction is inevitable within 60 years. For western monarchs, the chances are higher, 60%-68% within 10 years and 99% within 60 years. This estimate does not include potential catastrophic events, such as sea level rise or extreme temperatures.

The USFWS says it will continue to focus on conservation measures along with its partners. One conservation win for monarchs, enacted this year, was the Nationwide Candidate Conservation Agreement for Monarch Butterfly on Energy and Transportation Lands (CCAA).

Under the CCAA, more than 45 transportation and energy companies, as well as dozens of private landowners, agreed to create or maintain monarch butterfly habitat along “rights-of-way” corridors across the United States.

“The listing decision today highlights the importance of new and ongoing conservation efforts to support monarchs,” Iris Caldwell, a program manager at the Energy Resources Center at the University of Illinois at Chicago, one of the creators of the initiative, told Mongabay. “We have seen good momentum around the monarch CCAA so far this year, and we anticipate that the listing decision will encourage others to join the agreement and make voluntary long-term commitments to help monarchs.”

Citation: U.S. Fish and Wildlife Service. 2020. Monarch (Danaus plexippus) Species Status Assessment Report. V2.1 96 pp + appendices.

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

Mongabay is a nonprofit environmental science and conservation news platform that produces original reporting in English, IndonesianSpanish, and Brazilian Portuguese by leveraging over 500 correspondents in some 70 countries. We are dedicated to evidence-driven objective journalism.

This story originally appeared on Mongabay on Dec. 16, 2020, and is published through the Institute for Nonprofit News network.

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