First, the bleak butterfly news: The population of monarchs surviving the winter in Mexico appears to have fallen. Now, the good news: Researchers are working to figure out what makes a successful urban monarch garden, and it's not too early to start preparing one for this summer.
The area covered by monarchs in Mexico has decreased by more than a quarter compared with last season, according to Mexico's National Commission of Protected Natural Areas and World Wildlife Fund. Because the butterflies mass together on fir trees at their southern roosting grounds, populations are measured in hectares, or acres. This winter's count is only about 5 acres, down from nearly seven in 2019-20.
"When you have those really low numbers, you run the risk of a real catastrophic decline, like we've seen with the monarchs in California," said Erika Hasle, a conservation ecologist at the Field Museum in Chicago, where a community science project is heading into its third season. "We're not at that point yet with the monarchs east of the Rockies, but it's a real risk and it's a real concern. And it's an indication that there's something they're not getting."
The monarchs seen in the Midwest are part of the eastern population, which accounts for nearly all the monarchs in North America, and includes a supergeneration that flies thousands of miles to Mexico. The western population, which winters in California, was found to number fewer than 2,000 monarchs in a Thanksgiving count — a record low, down from nearly 30,000 the prior year and more than a million some years ago.
The news also follows a December finding from the U.S. Fish and Wildlife Service that monarchs are qualified to be listed under the Endangered Species Act but will have to wait their turn, as limited resources are directed to species with higher priority.
In the last 25 years, monarchs' populations have plunged by the hundreds of millions, according to the wildlife service's species status assessment report. The black and orange butterflies have to contend with insecticides, loss of milkweed — the plant monarchs lay eggs on and the caterpillars' sole food source — and habitat loss. They're also up against climate change and weather extremes.
The dwindling population led Field Museum researchers to ask: What makes a successful urban monarch garden? Hasle and Geographic Information System specialist Karen Klinger are working to answer that question.
Many stops along the monarchs' multigenerational migratory route are taking an all-hands-on-deck approach to helping out the butterfly, looking for more places where milkweed could grow. What happens in the migration path area can be crucial to the success of the generation that will make the long journey back to Mexico.
"How can a small piece of land do as much as possible for protecting this butterfly?" Hasle said. "Because we think to some extent, cities are providing an important refuge for a lot of insects."
But private residential spaces can be hard to track, so community science allows for access. The Field Museum project involves city dwellers reporting on spaces that researchers can't walk into every day, like backyards, or sending dispatches from their decks. The data contributes to a national monitoring project, which helps fill out the bigger picture.
"We're really finding habitat that we would not have known existed if people hadn't invited us into their yards and their balconies," Hasle said.
Although the Field Museum's project is fairly new, there are some findings after a pilot and pandemic season. Unlike some other field work derailed by the coronavirus, the monarch project worked well with more people staying home to watch over their gardens.
Participants sent in weekly reports, including the makeup of their garden, and development of eggs and caterpillars.
The most prevalent kind of milkweed planted among project participants was common milkweed, and it was associated with the most eggs. And while participants planted close to the same amount of swamp and butterfly milkweed, they reported about four times as many eggs on swamp milkweed.
The more successful gardens had more milkweed and blooming plants, multiple milkweed species, and tended to be larger plots. But there were small victories.
Klinger said one participant with a single plant watched eggs transform all the way to a chrysalis. So, she said, "You just need one plant."
Another finding last year was that the number of caterpillars dropped, even though the number of participants in the study more than doubled.
The area had a hot, dry summer — its warmest on record — and Klinger said that could have affected the health of the milkweed plants. But reports also came in of predators eating caterpillars.
"Overall, the sense of why the population is declining is that it's not just one thing," Hasle said. "Insects probably are one of the canaries in the coal mine."
The reports out of Mexico noted this season's eastern population drop followed an increase in forest degradation, which was four times what it was the prior year — primarily from illegal logging, as well as trees hit by wind and drought. But they also said spring and summer weather conditions were tough for milkweed blossoms and egg development in the southern U.S., which limited reproduction.
Scientists continue to research the connection between climate change and butterflies. A study published March 4 in Science on western butterfly declines (see arkansasonline.com/313decline), which drew on community science data, found disappearances could be driven largely by rising autumn temperatures. Researchers speculate that warmer weather disrupts the breeding cycle or harms the plants they feed on.
For monarchs, northern habitat could be particularly important this season, depending on what conditions the butterflies find in Texas after this winter's extreme cold and storms.
START GROWING
But now is the perfect time for planning to plant some milkweed, Hasle and Klinger said. They recommend checking out native plant sales and preordering; milkweed can be in high demand come June.
There aren't many don'ts for starting up a milkweed patch, Hasle said, but one plant to avoid is tropical milkweed, a nonnative plant that flowers late in the season. The best garden is one you can sustain, Hasle said. And it can make for a fun family project.
"The best thing to do is what you can do," Hasle said. "One milkweed plant in a pot on your balcony is doing something."
Judith Rice, a retired teacher who lives in Skokie, Ill., participated in the project in its first two seasons, while growing her garden with more milkweed and more pollinator plants. Now she has so much common milkweed, she gives it away.
"I can remember the first year looking for them and it's like, oh my gosh, look, there's a little caterpillar," Rice said. "Or, there's an egg!"
Last summer, the garden relieved some of the stress of the pandemic.
"Once you start counting the eggs and you start seeing caterpillars, it gets more and more fascinating and more and more motivating," Rice said. "I'm looking forward to doing it again this year. It gives you something to look forward to during the dreary winter in Chicago."