Monarch butterflies are not considered endangered. But a new study shows they are dwindling.

Monarch butterflies continue to flutter dangerously close to extinction despite a decision late last year to remove the orange-and-black insects from the endangered species list, a new study has found.

An annual survey led by the World Wildlife Fund (WWF) of the recognizable species wintering in central Mexico found the second-lowest number of monarchs on record. This year’s estimate found the eastern monarch butterfly colonies took up just 2.2 acres of regional forests, which is 59% less than during the 2022-2023 winter season.

The findings are troubling to ecologists intent on preserving the dwindling species. In October, the International Union for Conservation of Nature opted to change the butterfly species' status to vulnerable about a year after the organization declared the migratory monarch butterfly to be endangered.

"Fewer monarchs hibernating in their traditional forest habitat in Mexico greatly concerns all of us," Jorge Rickards, general director of WWF Mexico, said in a statement. "This is not the first time we've observed changes in the locations of the largest monarch colonies."

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How the World Wildlife Fund made the findings

The World Wildlife Fund's survey is considered to be a benchmark for ecologists to understand the overall abundance of the species. Experts with the organization and its myriad partners measure the area of forest in which monarch butterflies hibernate each winter to understand their estimated population status.

Each winter, monarch butterflies migrate for thousands of miles from southern Canada and the northern and central U.S. to spend winter in the mountain forests of central Mexico.

Ecologists with the World Wildlife Fund painted this winter season's findings as grave, explaining that they represent the second-smallest area occupied by monarch butterfly colonies in Mexico since 1993, when population monitoring began. Only 2013-2014 saw a smaller population size, with scientists estimating that 1.7 acres were occupied by the species.

The largest recorded population was in the 1996-1997 season, when the monarch butterflies were estimated to occupy 45 acres, according to the WWF.

Why the dwindling monarch butterfly population matters

Due to the high heat and drought brought on by climate change, the monarch's natural habitat is quickly depleting, scientists say.

Monarch butterflies require a large and healthy forest to protect them from winds, rain and low temperatures in the areas where they migrate for winter. A rich biodiversity defines these forest ecosystems, which are home to 132 bird species, 56 mammal species, 432 species of vascular plants and 211 species of fungi, the World Wildlife Fund said.

Scientists believe that climatic variations in the monarch's breeding areas in Canada and the U.S. gave rise to high temperatures and drought.

But in recent years, the monarch's breeding areas in Canada and the U.S. have seen a reduction in poisonous milkweed leaves where female monarchs lay their eggs.

"Land-use changes in the United States, combined with the widespread use of herbicides, also contributed to the loss of milkweed and other nectar plants essential to feeding adult monarchs," the WWF said.

While not the most prolific pollinators, monarch butterflies still play a vital role in sustaining plant ecosystems, according to the Monarch Joint Venture, a partnership of federal and state agencies, non-governmental organizations and academic programs intent on saving the species. The species is also an important food source for birds, small animals, and other insects, according to the National Park Service.

In a press release announcing its findings, the World Wildlife Fund asked for further research and conservation efforts concerning monarch butterflies.

"It's critical that all communities, governments, non-governmental organizations, scientists, and others continue to strengthen our conservation and protection efforts to support the monarch's unique migration," Rickard said in the statement. "It's telling us that we need to intensify conservation and restoration measures."

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at elagatta@gannett.com