A beloved visitor to summer gardens is officially an endangered species.

The migratory monarch butterfly—the iconic subspecies common to North America—was declared endangered today by the International Union for the Conservation of Nature (IUCN), the global leading authority on the status of biological diversity.

The butterfly, known for its twice-yearly, 2,500-mile journey across the continent between its summer and winter grounds, has declined by between 23 and 72 percent in the past 10 years, according to the IUCN.

Though the monarch has long been considered under threat, its listing on the IUCN Red List—the inventory of species’ conservation status—marks the first time it has been officially declared at risk of extinction.

“It’s hard for people to imagine that something that shows up in their backyard is threatened,” says Anna Walker, who led the monarch butterfly assessment. She’s a member of the IUCN Species Survival Commission Butterfly and Moth Specialist Group, and species survival officer at the New Mexico BioPark Society.

The threat to monarchs comes from a combination of factors. Habitat destruction over decades in migratory monarchs’ wintering grounds has taken a massive toll. The impact is felt by both the western population, which is found west of the Rocky Mountains and winters on the California coast, and the eastern population, which is found in the eastern U.S. and Canada and winters in Mexico’s fir tree forests. In summer habitats, pesticides used in agriculture have killed monarchs and also milkweed, the plant they lay larvae in. Climate change, too, is an increasing threat as dramatic weather events such as hurricanes and drought become more common along the butterflies’ southern migration routes.

The western monarch population, less studied and more at risk, has plummeted 99.9 percent in recent decades, from around 10 million in the 1980s to just 1,914 in 2021, according to the IUCN. The eastern population declined by 84 percent between 1996 and 2014.

Only one percent of insect species have been assessed by the IUCN—so having the monarch listed is significant. The listing can be a great tool to communicate to the public, and to global authorities, about the urgent need to conserve the butterfly, says Walker.

Bad news for sturgeons, good news for tigers

The IUCN also announced today that all species of sturgeons—26 in total—are now at risk of extinction, and 17 of those are critically endangered. One species, the Yangtze sturgeon, is now extinct in the wild.

Sturgeons are considered to be living fossils because the fish remain largely unchanged since the earliest fossil records. They date back 145 million years, and coexisted with dinosaurs.

For centuries, sturgeons have been overfished for their meat and caviar. While all sturgeon species are protected under international trade law, more than half continue to be poached and sold as delicacies. Stronger enforcement of illegal fishing and sales is crucial to stopping the trade, according to the IUCN.

The IUCN announcement did offer good news for some species, including the tiger. New data indicate there are between 3,726 and 5,578 tigers living in the wild, 40 percent more than the population estimated in 2015. This improvement mostly comes from improvements in monitoring as opposed to a tiger baby boom. But the IUCN says this is nevertheless a good sign that tigers, while still endangered, are stable and potentially increasing in numbers, thanks to conservation efforts. (Read about a dense Indian forest where tigers are thriving.)

Hope for monarchs

For the new assessment, Walker and colleagues analyzed a huge swath of data on monarch numbers from a variety of sources, which helped reconcile some differences, she says.

A recent, controversial study based on citizen-science data from summer nesting sites suggests that monarch butterflies may be increasing in some U.S. locations. It’s winter data, though, that is most telling, Walker says: “Even if populations are rebounding in some places during the summer, if overwintering populations continue to decline—or even remain stable—they remain precariously low.”

The past winter, however, offered some hope. A community-science count of butterflies at 283 winter nesting grounds in California, led by the Xerces Society for Invertebrate Conservation, saw a rebound for the western monarch butterfly: 250,000 butterflies were recorded, up from 1,914 in 2021. Winter counts are the most reliable way to monitor populations, Walker says, because nesting sites are massed in a small area, making counts more reliable.

Nonetheless, “when you think that there were three to 10 million butterflies in winter in the 1980s, and now there are 250,000,” she says, the overall trend in winter data is not promising.

“We thought it would be good to take all data—some is contradictory—and put it in this global context. That way, we’re using a standardized process” that isn’t influenced by political or social factors, she says. (Read about why the U.S. declined to list the monarch butterfly under the Endangered Species Act in 2020)

There is hope for the resiliency of monarchs too, Walker says. Insects reproduce quickly “so that gives a great opportunity: If we reduce some threats, the butterfly can do the rest of the work,” she says.

“We are kind of at this critical window where climate change is going to start having a bigger and bigger impact on species,” she says—so increasing the population numbers now may be critical to setting the butterflies up for success.

The fact that migratory monarchs are backyard insects means that everyone can pitch in. In North America, planting native milkweed (not tropical, which always stays green and can trick monarchs into choosing not to migrate for winter) is a great way to help them thrive, she says.

Given that “there’s still so much we don’t know” about monarchs, getting involved in community science programs that track and protect the butterflies locally is another way to help, she says.

“Unfortunately, it wouldn’t be the first time a widespread, common species can decline really quickly and disappear from the face of the Earth,” Walker says—a reference to the passenger pigeon, a once-ubiquitous bird that went extinct in the wild in 1914.

But unlike a century ago, today there’s unprecedented awareness of the biodiversity crisis. And that can spur action on behalf of threatened species, Walker says, if people care enough: “I do think the monarch has the power to do that.”