The monarch, a pollinator, has long been a symbol of conservation for everyday people, and one that scientists say is threatened by climate change, herbicide use and habitat destruction. But a new study published June 10 by researchers, including two from the University of Georgia, suggests the species may not be as threatened as previously thought.
Research over decades has shown populations of monarchs that spend their winters in warmer climates have been on the decline, but the new study suggests those losses are being offset by growth in some of the butterflies’ breeding populations — for now, at least.
Monarchs spend summers in the U.S. West, Midwest, Northeast and southern Canada, then migratory populations travel to California and Mexico for winter, according to the U.S. Forest Service.
Researchers analyzed more than 135,000 observations of the butterfly species from summer counts by citizen scientists with the North American Butterfly Association from 1993-2018.
According to the study published in the peer-reviewed scientific journal Global Change Biology, the researchers’ results suggest monarch populations overall rebound in the summer, compensating for losses in the winter. While the Northeast and Midwest have seen declines, the scientists found parts of the Southeast and Northwest have seen stable or increased numbers. Breeding populations are not showing strong evidence of widespread declines, the researchers found.
Overwintering monarch populations in Mexico and California have plummeted since scientists began studying them in the 1990s, and most studies focus on these sites. But Andy Davis, a research scientist at UGA who was part of the latest study, said he thinks this data is only a “snapshot” of the population.
“The problem with doing it that way is that not all of the monarchs are able to successfully reach the wintering colonies,” Davis said. “That’s the big assumption here: That assessing these wintering colonies, that you’re counting everybody. But you’re not really. You’re counting only the ones that made it.”
Scientists have pointed to the dangers to monarch butterflies for years, from herbicide use to climate change. Anurag Agrawal, professor of environmental studies at Cornell University, said the new study supports other recent findings that these variables have a role in long-term population trends. Agrawal gave feedback to the researchers for an early version of the study.
“Indeed, the monarch butterfly population does fluctuate a lot, and there are serious threats, but the prognosis based on this analysis is more that the population dynamics are changing than spiraling downward,” Agrawal wrote in an email to the AJC. “Monarchs are in trouble: they are more diseased, less migratory, and probably a little confused. But, they are not going extinct.”
However, other researchers also not involved with the study were more cautious in their interpretation.
Karen Oberhauser, a professor and the director of the Arboretum at the University of Wisconsin-Madison, said she agrees with the conclusion that weather and temperature have a varying effect on the population of monarchs, but she took issue with some of the methods used.
She said the continent-wide study uses lots of data — more than 135,000 observations were recorded — but the analysis isn’t nuanced because of the type of mathematical analysis and a limited annual period of study. Additionally, Oberhauser took issue with the scope of some of the data included.
Oberhauser said monarchs stay in the North or West during the summer, so the study may have missed when they’re at their greatest abundance in the South because they have already migrated through the region. She also noted that 2018 — the last year of data that the researchers analyzed — was an unusually good year for monarch populations.
Nevertheless, she agreed with one of the main assertions of the study that other butterfly species fare worse than monarchs. Those species deserve more attention.
“I think that’s a really legitimate point to make,” Oberhauser said. “I am a conservation biologist, and I care about all biodiversity.
“I’ve been studying monarchs since 1985,” she said. “...I think that monarchs are a connector for people. So if monarchs get people out counting butterflies, and if monarchs get people out and caring about habitat and trying to increase the amount of habitat, that’s going to benefit all species.”
The June 10 study found that although the monarchs’ situation may not be as dire as previously thought, climate change could threaten that. On the one hand, a rise in temperatures in certain areas could make colder regions, like Canada, more hospitable and expand the breeding range, Davis said. On the other, this could mean that the monarchs must migrate farther to overwintering sites.
“It’s almost like extending the length of the marathon by pushing the start line back,” Davis said, adding that he remains concerned about “the long-term stability” of the insects’ migration.
Raiford, the butterfly enthusiast from Sandersville, has bonded with her grandson over the winged creatures.
“The monarch was something that I could visualize, that I could see the miracle,” Raiford said. “If we’re killing the habitat for the monarch, we’re no doubt killing the habitat for the other butterflies as well.”
-Staff writer Drew Kann and freelancer Meris Lutz contributed to this report.
A note of disclosure
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