Monarchs in western US risk extinction, scientists say

Sept 7 (Reuters) - Monarch butterflies west of the Rocky Mountains are teetering on the edge of extinction, with the number withering in California down more than 90 percent from the 1980s, researchers said in a study published on Thursday.

While much is known about the black-and-orange winged insects' decadeslong population decline in the eastern United States, scientists have been unable to track the western variety accurately until the recent development of new statistical models.

The new study, published in the scientific journal Biological Conservation, was funded by the U.S. Fish and Wildlife Service, which is considering giving monarch butterflies Endangered Species Act protections.

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A monarch butterfly is pictured as it sits on a milkweed flower in North Miami Beach, Florida, U.S., September 14 2016. REUTERS/Carlo Allegri
A Monarch butterfly rests on a visitor's hand during the official Inauguration of the month of the Monarch butterfly at Chapultepec Zoo in Mexico City, Mexico, April 6, 2017. REUTERS/Edgard Garrido
A Monarch butterfly clings to a plant during the official Inauguration of the month of the Monarch butterfly at Chapultepec Zoo in Mexico City, Mexico, April 6, 2017. REUTERS/Edgard Garrido
A Monarch butterfly rests on a visitor's hand during the official Inauguration of the month of the Monarch butterfly at Chapultepec Zoo in Mexico City, Mexico, April 6, 2017. REUTERS/Edgard Garrido
Monarch butterflies cling to a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. Monarch butterflies may warrant U.S. Endangered Species Act protection because of farm-related habitat loss blamed for sharp declines in cross-country migrations of the orange-and-black insects, the U.S. Fish and Wildlife Service said. REUTERS/Michael Fiala (UNITED STATES - Tags: ANIMALS ENVIRONMENT POLITICS)
A monarch butterfly rests on a rope at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. Monarch butterflies may warrant U.S. Endangered Species Act protection because of farm-related habitat loss blamed for sharp declines in cross-country migrations of the orange-and-black insects, the U.S. Fish and Wildlife Service said. REUTERS/Michael Fiala (UNITED STATES - Tags: ANIMALS ENVIRONMENT POLITICS)
Hundreds of Monarch butterflies line a pine tree's branches on the Cerro del Campanario, in the El Rosario butterfly sanctuary, on a mountain over 3000 metres above sea level (9000 feet) in the Mexican state of Michoacan March 11, 2003. The Monarchs are the only migratory insects in their species and they travel 4000 kilometres (around 2500 miles) twice a year between their summer home in [Canada] and their winter home in Mexico.
Hundreds of Monarch butterflies line a tree trunk on the Cerro del Campanario, in the El Rosario butterfly sanctuary on a mountain over 3000 metres above sea level (9000 feet) in the Mexican state of Michoacan, March 11, 2003. The Monarchs are the only migratory insects in their species and make the 4,000 km (2,500 miles) journey between their summer home in Canada and their winter home in Mexico twice a year.
Hundreds of Monarch butterflies line a tree trunk, as others fall away on the Cerro del Campanario, in the El Rosario butterfly sanctuary, on a mountain over 3000 metres above sea level (9000 feet) in the Mexican state of Michoacan March 11, 2003. The Monarchs are the only migratory insects in their species and they travel 4000 kilometres (around 2500 miles) twice a year between their summer home in [Canada] and their winter home in Mexico.
JEFFERSON COUNTY, CO - MAY 25: A viceroy butterfly clings to a flower at the Butterfly Pavilion and Denver Botanic Gardens fourth annual habitat experience Butterflies at Chatfield Farms May 25, 2017 in Jefferson County. Over 300 native Colorado butterflies including the monarch, painted lady, common buckeye, queen, black swallowtail, viceroy and red admiral were released into the habitat, which is open to the public starting Saturday May 27, 2017 through September 24, 2017 daily from 9 a.m. to 4 p.m., with last entry at 3:15. (Photo by Andy Cross/The Denver Post via Getty Images)
Pam Spencer, right, a nurse and a self-taught expert on monarch butterflies, raises the butterflies at her home. Kyle Reedholm, 9, left, a former pediatric patient of hers, has helped with butterflies for the past year. (Algerina Perna/Baltimore Sun/TNS via Getty Images)
ANGANGUEO, MEXICO - DECEMBER 18: A monarch butterfly perchs on a twig at the Sierra Chincua sanctuary on December 18, 2015 in Angangueo , Mexico. The number of monarch butterflies reaching their wintering grounds in central Mexico this year may be three or four times higher than the previous year, according to environmental authorities. (Photo by Miguel Tovar/LatinContent/Getty Images)
A Monarch butterfly (Danaus plexippus) is pictured at the oyamel firs (Abies religiosa) forest, in Ocampo municipality, Michoacan State in Mexico on December 19, 2016. Millions of monarch butterflies arrive each year to breed at the oyamel firs forest in Michoacan State, after travelling more than 4,500 kilometres from the United States and Canada. / AFP / ENRIQUE CASTRO (Photo credit should read ENRIQUE CASTRO/AFP/Getty Images)
ANGANGUEO, MEXICO - DECEMBER 18: A monarch butterfly feeds on a plant at the Sierra Chincua sanctuary on December 18, 2015 in Angangueo , Mexico. The number of monarch butterflies reaching their wintering grounds in central Mexico this year may be three or four times higher than the previous year, according to environmental authorities. (Photo by Miguel Tovar/LatinContent/Getty Images)
A monarch butterfly rests on a piece of moss at the Sierra Chincua Butterfly Sanctuary near Angangueo in the state of Michoacan, Mexico, on Saturday, Jan. 17, 2015. Climate change and increased use of herbicides are threatening the monarch migration as well as eco-tourism in the region which attracts 120,000 visitors annually, according to scientists at the World Wildlife Fund in Mexico. Photographer: Susana Gonzalez/Bloomberg via Getty Images
Monarch butterflies fly near Oyamel trees at the Sierra Chincua Butterfly Sanctuary near Angangueo in the state of Michoacan, Mexico, on Saturday, Jan. 17, 2015. Climate change and increased use of herbicides are threatening the monarch migration as well as eco-tourism in the region which attracts 120,000 visitors annually, according to scientists at the World Wildlife Fund in Mexico. Photographer: Susana Gonzalez/Bloomberg via Getty Images
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Monarchs, which depend on a diminishing supply of milkweed plants for reproduction and food, are arguably the most popular of North America's butterflies and have a huge international following among students and scientists. However, the western population has fallen to about 300,000 from 10 million less than four decades ago.

"If the population continues to decline at that rate, we will lose migratory monarchs in the western United States over the next several decades," Washington State University biologist Cheryl Schultz, the study's lead author, said in a telephone interview.

The migratory monarchs of the western United States have a 63 percent chance of extinction in 20 years and an 84 percent chance in 50 years if current trends continue, according to the study.

Scientists believe declines in U.S. monarch populations are linked to human development that has wiped out their habitats, as well as the destruction of roosting forests in California and Mexico, climate change and farmers' increasing use of pesticides that kill milkweed plants and other native vegetation.

"The change has been so dramatic that if we don't act to protect them, they are threatened with extinction," said Tufts University ecologist Elizabeth Crone, a study co-author.

The western monarchs winter in coastal tree groves in California, only to fan out in spring to lay eggs on milkweed and feed on flowers there as well as in Arizona, Idaho, Nevada, Oregon, Utah and Washington.

By pairing counts of monarchs wintering in California with historical estimates, researchers determined the decline of the western population was steeper than previously believed.

The eastern and central U.S. population of monarchs, numbering in the tens of millions, is the most studied and is famed for its Mexico-to-Canada migration.

(Reporting by Laura Zuckerman; Editing by Ben Klayman and Lisa Von Ahn)

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