monarch butterfly roost
This roost of an estimated 1,200 monarch butterflies was photographed on Oct. 29 in Burnet, Texas, near Lake Buchanan. Credit: Courtesy of Jack Marshall

Robust numbers of butterflies and a population that’s lingering in and around San Antonio into November suggest the 2021 monarch butterfly migration season could be a good one.

Monarch numbers have been strong all season east of the Rocky Mountains where the monarch population migrates to Mexico. And in Central and South Texas, in what’s known as the “Texas funnel,” monarchs continue to move south somewhat later than normal into mid-November, especially along rivers or in landscapes where late-season flowers offer nectar for fueling the butterflies’ long flight to their winter roosting sites in Mexico.

Cathy Downs, a Comfort-based monarch butterfly conservation specialist for citizen science organization Monarch Watch, which tracks the butterflies’ migration each fall, described this year’s migration as “long and late.”

The multi-generation monarch migration typically starts in early March in Mexico and unfolds over the spring and summer, ending in late October with the butterflies moving through San Antonio en route to their winter roosting sites by early November.

Throughout October Downs has witnessed dozens of monarch butterflies at local parks in Kendall County, where peak monarch migration occurs in mid- to late October. The butterflies typically arrive in the mountains west of Mexico City in time for Día de los Muertos.

On Oct. 30, Downs got word that an estimated 1,200 monarch butterflies were roosting in Burnet, about 55 miles northwest of Austin, in the middle of a group of homes near Lake Buchanan.

“I was surprised by the size of the roost,” said Downs, adding that she traveled to Burnet to help tag the butterflies, but they dispersed quickly. Warm temperatures in the Northeastern U.S. this fall appear to be holding large numbers of monarchs back, extending the migration into November.

Juan Guerra, senior horticulturist for the City of San Antonio, said he’s noticed a difference in the migration this year.

“Monarchs came more in waves since late July rather than a mass migration in the fall and you can still see them today feeding from our nectar plants in our River Walk pollinator gardens,” he said.

This late presence of monarch butterflies is not just happening in Texas.

Don Davis, a longtime monarch butterfly follower in Ontario, Canada, where the multi-generation autumn migration begins, reported via an email list for monarch butterfly enthusiasts that monarchs were spotted in Point Pelee, Ontario, on Nov. 8.

“These sightings are uncommon,” said Davis. “Most regions of Ontario have now had their first frosts, but a few monarchs seem to survive overnight, possibly finding a sheltered spot or microhabitat in which they survive.”

Out on the West Coast, where a separate population of monarch butterflies migrates up and down the California coastline, the news also has been upbeat. Numbers of the iconic creatures plummeted to less than 2,000. But now the insects have rebounded handsomely, despite drought, wildfires, and the recent bomb cyclone.

“It’s a hopeful sign that we are seeing better numbers and the migration is definitely not gone, as some feared after last year,” said Emma Pelton of the Portland, Oregon-based Xerces Society, an invertebrate conservation and protection organization that filed a petition in 2015 to have monarch butterflies listed as “threatened” under the Endangered Species Act. The species was denied that status in December 2020.

Monarch butterfly takes nectar from a Gregg’s Purple mistflower in front of the San Antonio River Authority office along the San Antonio River on Nov. 8. Credit: Monika Maeckle / For the San Antonio Report

Even though the recent uptick in monarch numbers appears positive, Pelton said it does not constitute a population recovery.

“If this was four years ago, we would actually be quite concerned with how low the numbers are,” she said. “It’s really important not to get used to a new baseline and forget that we had hundreds of thousands of monarchs in the 2000s and 2010s and over a million monarchs in the 20th century.”

Karen Oberhauser, founder of monarch butterfly citizen science organization Monarch Joint Venture and professor of restoration ecology at the University of Wisconsin-Madison, said she’s cautiously optimistic about summer breeding activity and anecdotal reports of high numbers seen during the fall migration.

“I hope … it translates into good numbers in Mexico,” she said. She added that the news from California is “incredibly exciting.”

Chip Taylor, founder of Monarch Watch, was less enthusiastic and suggested that the eastern monarch migration population will decline this year. He pointed out that late migrations historically make for smaller overwintering populations.

“As to the East, numbers are down, and the overwintering population numbers will be substantially lower this year,” he said.

David James, an entomologist at Washington State University who studies the California population, sees a hopeful future of mixed monarch populations. As the climate continues to warm, some will migrate, and others will stay put. “The proportion and population sizes of these will shift annually according to temperatures, particularly during September and October,” he said.

Another reason entomologists and monarch enthusiasts are optimistic: The recently passed national infrastructure bill, which awaits President Joe Biden’s signature, includes the Monarch and Pollinator Highway Act of 2021.

The act will provide for $2 million annually from 2022 to 2028 for grants to carry out pollinator-friendly practices on roadsides and highway rights-of-way, including the planting and seeding of native, locally appropriate grasses, wildflowers, and milkweed. The grants will be available to states, American Indian tribes, and federal land management agencies.

Monika Maeckle

San Antonio Report co-founder Monika Maeckle writes about pollinators, native plants, and the ecosystems that sustain them at the Texas Butterfly Ranch website. She is also the founder and director of...