Monarch Butterflies Wintering in Mexico Drop to Second-Lowest Level Ever Recorded

Monarch butterflies during overwintering season at the Monarch Butterfly Biosphere Reserve in Michoacán, Mexico on Feb. 23, 2017. Sylvain CORDIER / Gamma-Rapho via Getty Images

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The estimated number of monarch butterflies migrating to Mexico for winter has reached its second-lowest level ever for the 2023 to 2024 overwintering season. The estimate, based on the size of the butterflies’ hibernating forest area, has dropped by about 59% from the previous year, according to officials.

Experts are pointing to extensive heat and drought as well as climate change for the major decline.

Recent years have seen some hope for the migrating monarch butterflies, with a 35% increase in the number of butterflies observed overwintering in Mexico during the 2021 to 2022 season compared to the previous year. 

But monarch butterflies face three primary threats, including habitat loss for their breeding and overwintering; the use of pesticides, which can be toxic to the butterflies or can kill their food source, milkweed; and climate change, which can shift their migratory patterns. By the 2022 to 2023 overwintering season, World Wildlife Fund reported a 22% drop in the amount of overwintering monarch butterflies in Mexico.

According to WWF, monarch butterflies once covered about 45 acres of forested land in Mexico during their 1996 to 1997 overwintering season. Last year, they covered 5.5 acres. With the 59% decline, the 2023 overwintering season saw the butterflies covering just 2.2 acres, The Associated Press reported. The lowest coverage ever recorded was 1.65 acres from 2013 to 2014.

The largest amount of butterflies observed for the current overwintering season were around the Monarch Butterfly Biosphere Reserve.

“This is not the first time we’ve observed changes in the locations of the largest monarch colonies,” Jorge Rickards, general director of WWF Mexico, said in a statement. “It’s telling us that we need to intensify conservation and restoration measures not only in the Monarch Butterfly Biosphere Reserve, but also outside of it.”

According to the Center for Biological Diversity, monarch butterflies have declined by 85% in the past 20 years. The eastern monarch butterflies migrate from Canada and the U.S. to Mexico for overwintering. Western monarchs, which overwinter in California, have declined 99% in the past two decades.

Monarch butterflies do not currently have federal protections. In 2020, the U.S. Fish and Wildlife Service noted that these butterflies do warrant protections under the Endangered Species Act, but there were higher-priority species to consider for listing. Biologist Ryan Drum, who works with the U.S. Fish and Wildlife Service, told The Associated Press that the latest count would be considered this year when officials consider whether to list migratory monarch butterflies as threatened or even endangered. 

According to the California Department of Fish and Wildlife, monarch butterflies are expected to receive protections later in 2024.

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