Study: Western monarchs’ decline is precipitous

Freshly emerged from their chrysalises, adult monarch butterflies sip nectar from the flowers of showy milkweed. Idaho Department of Fish and Game

A researcher prepares to tag a monarch butterfly. Idaho Department of Fish and Game

Monarchs can travel 100 miles a day during migration. This tagged monarch from southwest Idaho may provide answers to Idaho’s monarch flyway. Idaho Department of Fish and Game

Monarch butterflies do all all of their growing in the caterpillar stage. Idaho Department of Fish and Game

SALMON — Beth Waterbury, regional wildlife biologist here for the Idaho Department of Fish and Game, has spent a part of this and several summers tracking monarch butterflies, seeking to uncover the secrets of their life cycles and migrations in order to help save them.

It’s an ambitious goal and Waterbury is far from alone in spending untold hours collecting data on the iconic butterfly and the dwindling number of milkweed plants used by the creatures to lay eggs and provide early food for their young.

Ranks of professional researchers, citizen scientists, students and other monarch devotees have in recent years turned their attention to gathering information about the so-called western population of monarchs — or those west of the Rockies — after counts conducted in the coastal California tree groves where they winter showed a decline.

Unlike the so-called eastern population of monarchs, which embark on a multigenerational migration that sees them wing from Canada to Mexico each year, the butterflies in the U.S. West migrate from California to states including Idaho, Nevada and Utah to reproduce and gather nectar from flowers.

The decline among western monarchs is more severe than first thought. Research published online Thursday in the journal “Biological Conservation,” showed millions of the beloved orange-and-black-segmented butterflies once found refuge in the Golden State during the colder months but now monarchs that over-winter there are estimated to number 300,000.

The study, whose authors include Washington State University biologist Cheryl Schultz, Tufts University ecologist Elizabeth Crone and Emma Pelton of the Xerces Society for Invertebrate Conservation, relied heavily on information gleaned from annual counts of western monarchs organized by the Xerces Society and monitoring by citizen scientists.

Using recently developed statistical techniques, Schultz and her team of researchers learned that millions of monarchs likely wintered in California in the 1980s, but that number has dropped precipitously ever since.

The rate at which western monarchs have declined suggests they are at risk of extinction if steps are not taken to reduce such threats as habitat loss tied to urban, commercial and industrial development, changes in agricultural practices that either destroy milkweed plants through chemical applications or by crowding out patches where native plants once took root, and harvesting of the trees where monarchs find refuge in the winter, scientists said.

“Based on what we now know, there is a significant threat to the population. There is a significant risk that, if things stay the same, western monarchs probably won’t exist as we know them in 35 years,” Schultz said.

Led by the Xerces Society, petitions requesting monarchs come under federal protections were submitted to the U.S. Fish and Wildlife Service, which is considering adding the butterflies to the list of endangered and threatened species.

Meanwhile, scientists such as Waterbury are scrambling to bring into focus the life of the butterfly while it resides in states such as Idaho as well as the prevalence and type of milkweed plants monarchs rely on.

In a sign of the popularity of the monarch, admired for a delicate beauty and for its extensive migration, it is the state insect in Idaho as well as Alabama, Illinois, Minnesota, Texas, Vermont and West Virginia.

Idaho’s monarch and milkweed survey saw Waterbury and four technicians cover the state last year seeking milkweed patches and signs they were utilized by breeding butterflies.

Prior to that survey, researchers thought just a single of Idaho’s 10 climate divisions — notably the Snake Plain — possessed a season of sufficient length to support a generation or two of adult monarchs, Waterbury said.

“But we ended up finding monarchs in all of Idaho’s climate divisions. The discovery aspect of that was pretty cool,” she said.

This year, Waterbury has concentrated on state wildlife management areas because they show strong evidence of productive monarch breeding habitat, with naturalized and native milkweed plants in flood plains and wetlands.

While a variety of the plant known as showy milkweed is found more frequently in Idaho, a type called swamp milkweed also exists. Waterbury said work this season showed areas containing both types of milkweeds have the highest abundance of breeding monarchs.

Before the projects undertaken by Waterbury, Idaho had just a handful of historical records tied to monarchs.

“If we’re going to do any sort of conservation work aimed at monarchs, we need to know more about them and their habits,” she said.