Western Monarch Butterflies On Extinction Path After Record Low Winter

Possibly the most familiar and beloved butterflies in the world is on the verge of extinction in its western range, and the larger eastern population may follow. Image credit: Kenneth Dwain Harrelson CC-BY-SA-3.0

The future is dire for one of North America's biological wonders, following a 99 percent decline of the western monarch butterfly count at its wintering grounds in just four years

Like the passenger pigeon and the buffalo, the monarch butterfly was once a species whose migration symbolized the sheer abundance of nature. Billions upon billions of the fragile creatures fluttered barely believable distances across the continent twice a year, seeking food and warmth.

The larger migration occurs east of the Rocky Mountains. Even on the western side, however, attempts to count the butterflies resting in trees along the California coastline produced estimates in the millions in the 1980s. That was almost certainly a drastic decline from pre-European numbers, but alarm really started with a paper in Biological Conservation in 2017 recording a drop to 300,000. By 2018-19 the number had fallen to 27,000, at the time easily a record low. The decline came despite an increase in the number of sites surveyed. Last winter brought a little relief, rebounding slightly to 29,000.

This year the Xerces Society, which conducts the annual count, could not even find 2,000 butterflies west of the mountains. Some once-abundant sites reported no monarchs at all.

"These sites normally host thousands of butterflies, and their absence this year was heartbreaking for volunteers and visitors flocking to these locales hoping to catch a glimpse of the awe-inspiring clusters of monarch butterflies," the society's director of endangered species Sarina Jepsen said in a statement.

The monarchs can only lay their eggs on milkweed, and rely on nectar from a variety of flowers to fuel their travel. Much of the territory once covered by milkweed is now taken up with urban growth, and herbicides and pesticides affect most of the rest. This creates a long-term downward trend, accelerated by climate change. Last summer's California wildfires may have contributed to the sudden collapse this year.

The eastern monarch population is doing better, but has nevertheless suffered declines large enough to suggest it could eventually follow in its western counterpart's path.

Astonishingly, given their iconic status and rate of loss, monarchs lack protection not only at the federal level but in the most affected states as well. An assessment by the Fish and Wildlife Service found the monarch's listing under the Endangered Species Act “warranted, but precluded by higher priority actions”. Besides pushing for protection, the Xerces society encourages planting milkweed or other flowers that bloom early in the season, when food is needed most.

Monarchs can be counted so accurately in winter because they cluster at a few regular sites to keep each other warm. Although the western monarchs have never been anything like this low before, one scrap of hope comes from a brief but dramatic recovery in the mid-90s, showing their decline is not inevitable.

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