Saturday, December 3, 2022

Monarch butterfly population in decline due to agricultural practices and climate change

NewsMonarch butterfly population in decline due to agricultural practices and climate change
THE REVIEW
The monarch butterfly is one of the most recognizable insects in North America.

BY
Contributing Reporter

The monarch butterfly is one of the most recognizable insects in North America. The two geographic groups, western monarchs and eastern monarchs, have migratory patterns up to 2,800 miles, conducted over two to three generations. In Central Mexico during the fall, millions of eastern monarchs can be seen fluttering above the tree line in a frenzy of orange and black as they prepare for winter in the south. 

Lee Conway, a 21-year-old New Jersey resident, became inspired to raise monarchs after rescuing one with a broken wing. While the first monarch they saved died later that day, Conway had already decided to start raising caterpillars.

“It just struck me with how beautiful and magical they were,” Conway said.

Conway fed the caterpillars fresh milkweed everyday until they grew to be two inches long, at which point they would crawl to the top of the cage and form chrysalises, hatching as butterflies after eight days.

While millions of monarchs continue to hatch and migrate each year, over the past two decades, according to The Center for Biological Diversity, the eastern monarch population has declined by more than 80%. The U.S. Fish and Wildlife Service declared that the butterfly qualified for the threatened and endangered species list in December 2020, however there are 161 species that are listed as higher priority for protection.

A monarch butterfly will begin its life as an egg laid on a milkweed plant — these plants can be found bunched together in fields or along roadsides, standing five feet tall and adorned with pink, spherical flowers. This serves as the butterfly’s home and source of food, containing the cardiac glycoside that gives the monarch its colorful appearance. Cardiac glycoside is poisonous to animals when ingested, and the monarch’s aposematic coloration warns predators such as birds of its foul taste.

Farmers in the Midwest see milkweed as an invader that grows between the nooks and crannies of their crops and often plow it away or use herbicides to eliminate them, shrinking the monarch’s habitat and food source.

“The loss of milkweed in agricultural fields is a major cause of decline in Monarchs,” The Monarch Joint Venture wrote in a statement. “Herbicide application and increased mowing in roadside ditches and agricultural margins is eradicating milkweed habitat even more from rural areas.”

A 2017 study from the U.S. Geological Survey estimated that 3.86 billion stems of milkweed would be needed to stabilize the monarch butterfly population, with only 1.34 billion stems remaining in the United States. 

Climate change also contributes to the declining monarch butterfly population. National Geographic writer Carrie Arnold wrote the more carbon dioxide is in the atmosphere, the more cardiac glycoside is produced by milkweed, making the plant too toxic for the butterflies to ingest and store safely. Rising temperatures are also likely to have an effect on migration patterns.

“Higher temperatures may also be driving summer breeding areas further north,” Arnold wrote. “That means the monarchs’ migration routes will get longer and therefore more difficult.”

Monarch butterflies are sensitive to temperature and rely on environmental cues to tell when it is time for them to migrate and reproduce. When fall begins in North America, they begin their migration to Central Mexico, their overwintering site. They will huddle in trees in clusters together until winter is over then make their way back up north, laying eggs along the way. These eggs will hatch and continue the journey north to Canada bringing the process full circle. 

According to The National Oceanic and Atmospheric Administration’s 2020 annual climate report, the yearly North American temperature has increased 0.23°F per decade since 1910. 2020 marked the 44th consecutive year in which global land and ocean temperatures were above average. These temperature fluctuations are proving to be deadly to the monarch’s survival.

With climate change and increasing temperatures also comes increased precipitation. According to The Convention on the Conservation of Migratory Species and Wild Animals, increased rainfall has been found to reduce the amount of time monarchs spend laying their eggs, while extreme hurricanes can wipe out huge populations of them at a time in Mexico.

While raising a handful of monarchs is harmless, like Conway did, mass raising and releasing monarch butterflies — especially for events such as weddings and funerals — is not a good conservation strategy. Monarchs grown in captivity are less likely to survive and could spread diseases to other monarchs when released in the wild. 

A more effective strategy is a pollinator garden that both bees and butterflies can use. A pollinator garden consists of native milkweed and nectar plants per location with no additional use of herbicides. Even a singular pot of milkweed will function as a monarch waystation for them to sustain their migration and reproduction for generations. 

Inspired, Conway recently purchased milkweed that they will plant in the upcoming months for their own butterfly garden, remarking that the impact these monarch butterflies made on them was “spiritual” and something they will never forget.

“Nature is truly magic,” Conway said. “I have been deeply touched by these little yellow creatures.”

Currently there are no legal protections for monarchs or their habitats because they have not yet been listed as an endangered species, but are scheduled to be put on the list in 2024 should their numbers continue to decline.

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