The number wintering in California is down more than 90 percent from the 1980s

Monarch butterflies west of the Rocky Mountains are teetering on the edge of extinction, according to a new study featured in the articles below.

The study referred to is as follows:

Citizen science monitoring demonstrates dramatic declines of monarch butterflies in western North America
Cheryl B. Schultz, Leone M. Brown, Emma Pelton, Elizabeth E. Crone
Biological Conservation
Available online 7 September 2017
https://doi.org/10.1016/j.biocon.2017.08.019
http://www.sciencedirect.com/science/article/pii/S0006320717304809

The study mentions that among other factors, the “diminishing supply of milkweed plants for reproduction and food” is negatively impacting monarch populations. It is well established that this diminishment is largely due to the spread of GM glyphosate-tolerant crops. The glyphosate herbicides sprayed liberally on these crops kills milkweed, the monarch larvae’s only food.

While most GM corn and soy is grown in the Mid-West and is thus outside the scope of this Western US-focused study, some corn is grown in most US states.

1. Monarchs in western US risk extinction, scientists say
2. Monarch butterflies disappearing from western North America
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1. Monarchs in western US risk extinction, scientists say

Laura Zuckerman
Reuters, 7 Sept 2017
http://www.reuters.com/article/us-usa-butterflies-monarch/monarchs-in-western-u-s-risk-extinction-scientists-say-idUSKCN1BI2NA

Monarch butterflies west of the Rocky Mountains are teetering on the edge of extinction, with the number wintering 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’ decades-long 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.

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.
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2. Monarch butterflies disappearing from western North America

Phys.org, September 7, 2017
https://phys.org/news/2017-09-monarch-butterflies-western-north-america.html

Monarch butterfly populations from western North America have declined far more dramatically than was previously known and face a greater risk of extinction than eastern monarchs, according to a new study in the journal Biological Conservation.

"Western monarchs are faring worse than their eastern counterparts," said Cheryl Schultz, an associate professor at Washington State University Vancouver and lead author of the study. "In the 1980s, 10 million monarchs spent the winter in coastal California. Today there are barely 300,000."

Schultz adds, "This study doesn't just show that there are fewer monarchs now than 35 years ago. It also tells us that, if things stay the same, western monarchs probably won't be around as we know them in another 35 years."

Migratory monarchs in the west could disappear in the next few decades if steps aren't taken to recover the population, Schultz said.

Like eastern monarchs, which overwinter in Mexico, western monarchs have a spectacular migration. They overwinter in forested groves along coastal California, then fan out in the spring to lay their eggs on milkweed and drink nectar from flowers in Arizona, California, Nevada, Oregon, Washington, Idaho and Utah. They return to their coastal overwintering sites in the fall.

In the 1990s, residents of coastal California became alarmed that a once common butterfly seemed to be disappearing. The Biological Conservation study indicates that those concerns were justified. The researchers combined data from hundreds of volunteers who have participated in the Xerces Society's Western Monarch Thanksgiving Count since 1997 with earlier monarch counts conducted by amateur and professional butterfly enthusiasts in the 1980's and early 1990's. They then predicted the monarch population's risk of extinction over the next several decades.

Emma Pelton, endangered species conservation biologist at the Xerces Society for Invertebrate Conservation and co-author of the study, said the research will help conservationists better understand the extinction risk of western monarchs.

"Scientists, policy makers and the public have been focused on the dramatic declines in the well-known eastern population, yet this study reveals that western monarchs are even more at risk of extinction," Pelton said. "We will need significant conservation action to save monarch butterflies in the West."

The precise causes of the decline in western monarchs are not yet clear, but the loss and modification of its habitat and pesticide use across the West, where monarchs breed, are likely culprits, the researchers said. Climate change and threats to coastal California overwintering sites likely also play a role, they said.

The U.S. Fish and Wildlife Service, which funded the study, is currently considering whether to list the monarch butterfly as a threatened species under the Endangered Species Act.

Elizabeth Crone, Tufts University professor and a co-author on the study, says that "The hard part of being a conservation biologist is documenting species declines. The exciting part is figuring out how to help declining species recover. In the 20th century, we brought bald eagles back from the brink of extinction by limiting use of DDT. If we start now, we can make the 21st century the era in which monarchs return to our landscapes."