Despite dire warnings, monarch butterfly numbers are solidNew study shows warmer temperatures and increases during the summer are compensating for negative factors, stabilizing breeding trends
Date: June 10, 2022
Source: University of Delaware
Summary: Scientists have been warning for quite some time that monarch butterflies were slated for extinction due to diminishing winter colonies. But a new study found that warming temperatures and growth in the summer population of monarchs has compensated for losses during the winter. Researchers did preach continued caution, as the study did show continuing declines in other species of butterflies.
Largely because of well-publicized, diminishing winter colonies in Mexico and California, monarch butterflies across North America have been long thought to be declining as a result of diminishing summer habitat. Previous butterfly research shows that the size of overwintering monarch colonies has fallen across several decades. But what is happening when monarchs breed in the summer was less clear.
In a new research study published in Global Change Biology, lead author Michael Crossley, assistant professor and agricultural entomologist at the University of Delaware, and his collaborators examined trends in breeding monarchs across their entire range, and found there are local regions of decline, but also regions of increase. When considering the entire species range, there was no overall decline, and in fact, even a slight increase in abundance.
"The whole reason that we did this research is because monarch colonies have been declining," said Crossley. "Up until now, there were real fears that the monarch is in trouble."
The study's results suggest that population growth in summer is compensating for losses during the winter. Additionally, findings indicate that changing environmental variables have offsetting effects on deaths and reproduction.
North America's three largest countries have more in common than playing the 2026 hosts of soccer's biggest spectacle -- the FIFA World Cup. The perception of the monarchs' decline had prompted the U.S. Fish and Wildlife Service to determine if the species warrants a higher level of protection. Canada's equivalent agency is strongly considering listing monarchs as an endangered species because of the declines in Mexico.
As the researchers analyzed the data, patterns emerged and were location specific. Portions of the U.S. Northeast and parts of the Midwest revealed population declines. The U.S. Southeast and Northwest were unchanged or increasing, yielding a slightly positive overall trend across the species range. Monarchs in Florida appear to be doing exceptionally well.
"Our question was, 'Are monarchs declining across their breeding range?' The key take home message was yes, monarchs are declining in some places, but increasing in other locations," said Crossley, who conducts research and teaches in the UD Department of Entomology and Wildlife Ecology. "There is no consistent, long-term trend."
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Source:
https://www.sciencedaily.com/releases/2022/06/220610120224.htm
