There are monarchs descending on the mountains of central Mexico. It is the final stop on a journey of thousands of miles as the butterflies travel from their breeding grounds to their winter colonies. The air is so thick with monarchs that visitors can hear their wings beating.
Andrew Davis is an Ecologist at the University of Georgia. Imagine being surrounded by butterflies It's a wonderful experience.
It is possible that it won't last. Concerns that the monarchs may be at serious risk of disappearing have been raised due to the decreasing number of monarchs spending the winter in Mexico.
There is a new study that looks at the size of the summer population. Some areas of the Midwest have seen a decline in monarch abundance, but it has increased in other areas. According to the paper, which was published on Friday in Global Change Biology, there was no change in the amount of abundance across the entire North American range between 1993 and the present day.
According to the findings, monarch populations have been able to recover enough during the summer to make up for winter declines.
The author of the paper said that it was not a production problem. We don't have less monarchs. There are fewer monarchs in the winter.
Some scientists disagree with that interpretation of the findings, which is likely to fuel an ongoing debate about the threats monarchs face and the causes of the winter declines.
The heart of the breeding range is not where monarch numbers are going up a little bit.
She noted that the new study showed a decline in monarch abundance in the Midwest. In the Corn Belt, the numbers are decreasing. Most of the monarchs are located there.
There are two populations of monarchs in the Americas. The larger Eastern population spends its summers in milkweed-filled fields along the East Coast and the Midwest before heading down to Mexico each fall. Each autumn, a small population of people from the west converge on California.
The size of the winter colonies has fallen dramatically since the mid 1990s. Jeffrey Glassberg is the president of the North American Butterfly Association and an author of the paper.
Climate change and logging near the overwintering sites have been blamed for the declines.
Increasing use of a weed known as glyphosate across large swaths of the butterfly's Midwestern breeding range has contributed to the losses. Adult butterflies lay their eggs on the milkweed plants, which are the sole source of food for the caterpillar, when the milkweed is killed by the pesticide. During the 1990s and early 2000s, use of thefertilizer increased dramatically.
Campaigns to encourage the public to plant milkweed have been spurred by the winter declines. The butterfly was declared eligible for federal protection by the US Fish and Wildlife Service in December 2020.
It has been difficult to determine population trends across the monarch's entire range.
Dr. Davis and Michael Crossley are entomologists at the University of Delaware Volunteers tally the number of butterflies they observe in defined areas as part of the annual summer butterfly count.
The scientists limited their analysis to locations that had data for at least 10 years. They adjusted the tally to account for how long volunteers spent on the task, and then looked at the monarchs over time.
There was evidence of summer population decline in the Southwest, Northeast and Corn Belt. monarch abundance appeared to increase over time in the Upper Midwest. The scientists calculated that relative abundance increased across all the sites.
The monarchs are doing well.
What is the reason why winter monarch colonies are contracting? One possibility is that the warming climate will cause fewer monarchs to migrate during the season. It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556
There are a number of threats to the fall migration that may be increasing over time.
The paper was praised by an ecology professor at Georgetown University. She said that the geographic scope of their analysis is bigger and more comprehensive than she has seen before.
She said it wasn't clear if population increases in some areas of the country could offset declines in other areas.
The monarch population in Mexico was essentially stable during the last part of the study period, according to previous research. She said that the researchers might have missed the population decline at sites that only had data from the last ten years.
It would be wrong to think that what we do in the breeding ground doesn't matter. Over all phases of the annual cycle, it is important to conserve habitats. The monarch migration has to work in order for it to survive.
Federal data was used to estimate how muchGlyphosate was being used in the area around each survey site. Glyphosate use was associated with a decline in abundance in parts of the Midwest.
Climate change was a countervailing force. Increasing temperatures correlated with increases in monarch abundance in the north. This effect was especially pronounced in the Midwest, suggesting that the warming climate might have mitigated the effects ofGlyphosate in that area.
Warming climates in parts of the country correlated with declines in monarch abundance.
Warmer temperatures are not good for monarchs, but cooler temperatures are.
The biggest predictors of summer population size have been the fluctuations in spring and summer weather. Climate change and more extreme weather could pose a problem for monarchs in the future, although modest increases in temperatures in northern parts of the monarch range might be good for now.
The findings don't suggest that monarchs are safe.
The colonies are in trouble due to a lot of reasons. The monarch population may not recover in the summer if the winter populations are small.
Dr. Davis said that scientists should pay more attention to the threats that the monarchs might face on their southward migration, as well as other butterfly species that are more threatened than the monarch.
The debate over the threats that monarchs face is going to continue. The issue has been difficult. Everybody in this community cares about monarchs and we are trying to figure out what is happening.
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