MEXICO CITY — The number of monarch butterflies wintering in the mountains of central Mexico dropped 22% from the previous year, and the number of trees lost from their favored wintering grounds tripled.
Frost and “extreme temperatures” in the United States may have played a role in the butterfly’s decline during the most recent winter season, said Humberto Peña, director of Mexico’s nature reserves.

Marco Ugarte, Associated Press
Monarch butterflies gather on a shrub at Piedra Herrada sanctuary in the mountains Jan. 4 near Valle de Bravo, Mexico.
Monarchs east of the Rocky Mountains in the United States and Canada overwinter in the fir forests of the western state of Michoacan, west of Mexico City. The total area they occupied this past winter dropped to 5.4 acres, from 7 acres a year earlier.
The annual butterfly count doesn’t calculate the individual number of butterflies, but rather the number of acres they cover when they clump together on tree boughs.
Gloria Tavera, conservation director of Mexico’s Commission for National Protected Areas, said the area of forest cover appropriate for the butterflies that was lost rose to 145 acres, from 46.2 acres last year.
Illegal logging has been a major threat to the pine and fir forests where the butterflies gathering in clumps to keep warm. But experts said that this year, more than half the tree loss was due to removal of dead or sick trees affected by fires, storms or pests. Tavera said a lack of rain had plunged trees into hydric stress, making them more vulnerable to diseases, pests and fires.
Jorge Rickards, Mexico director of the WWF conservation group, blamed climate change,
“The monarch butterfly is an indicator of these changes,” Rickards said.
Critics say that in the past, removal of diseased trees has been used as a pretext for felling healthy trees for timber.
Tavera said she had no evidence that occurred this year, adding, “I don’t think anyone is lying.”
Each year the monarchs return to the United States and Canada on an annual migration that is threatened by loss of the milkweed they feed on north of the border and by deforestation in the butterfly reserves in Mexico.
Due to many factors, monarch numbers have dropped in recent years. Experts say drought, severe weather and loss of habitat — especially of the milkweed where the monarchs lay their eggs — as well as pesticide and herbicide use and climate change all pose threats to the species’ migration.
Illegal logging also continues to plague the reserves, and Peña said there are plans to station National Guard troops in the reserve to prevent it.
But open, illegal tree cutting actually dropped 3.4% this year, largely due to the efforts of inhabitants to protect their forests, a change of attitude by many.
For example, on Jan. 23, the communal farm community of Crescencio Morales — once the area with the worst illegal logging — fielded its first class of trained and officially approved forest rangers.
The 58-strong forest ranger “Community Guard” of Crescencio Morales began life several years ago as a rag-tag band of farmers armed with a motley collection of weapons, before the state government offered to train and equip them.
The community’s struggle began in the early 2000s, when residents fought to kick out drug traffickers and illegal loggers and redeem itself in the process.
“Back in 1998, the inhabitants of Crescencio Morales decided to set fire to the monarch butterfly colonies, in order to log the land,” recalls Erasmo Álvarez Castillo, the leader of the communal, or ejido, farmers in the village.
Residents quickly saw two things: The illegal logging brought with it the incursion of drug cartels and surrounding communities were making money off tourism.
So starting around 2000, the farmers began reforesting the mountain slopes. But they still had to expel the drug gangs. It was a long and arduous fight that eventually forced the farmers to take up arms, after calls to police for help in defending the community went unanswered.
Things came to a head when the town declared itself an autonomous, self-governing municipality.
Faced with armed, rebellious farmers, the government decided to try to professionalize the community force and train it to protect the forests.
Now, with the butterflies back, the village can dream of attracting tourists.
“The land we have on the mountaintop is very beautiful. It would be good for a tourism site,” Álvarez Castillo said. “The plan is to make trails, put up cabins — a tourist site without destroying the environment.”
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Number of monarch butterflies wintering in Mexico drops 22%
Robert F. Bukaty
A monarch butterfly flies to Joe Pye weed, Wednesday, Aug. 28, 2019, in Freeport, Maine. The populations of both insect species have struggled in recent years. Rapid development and climate change are escalating the rates of species loss, according to a May United Nations report. (AP Photo/Robert F. Bukaty)
Robert F. Bukaty
A monarch butterfly flies to Joe Pye weed, Wednesday, Aug. 28, 2019, in Freeport, Maine. The populations of both insect species have struggled in recent years. Rapid development and climate change are escalating the rates of species loss, according to a May United Nations report. (AP Photo/Robert F. Bukaty)
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Number of monarch butterflies wintering in Mexico drops 22%
Robert F. Bukaty
A monarch butterfly is buzzed by a bumblebee as it sips nectar on a Joe Pye weed, Wednesday, Aug. 28, 2019, in Freeport, Maine. The populations of both insect species have declined sharply in recent years. Rapid development and climate change are escalating the rates of species loss, according to a May United Nations report. (AP Photo/Robert F. Bukaty)
Robert F. Bukaty
A monarch butterfly is buzzed by a bumblebee as it sips nectar on a Joe Pye weed, Wednesday, Aug. 28, 2019, in Freeport, Maine. The populations of both insect species have declined sharply in recent years. Rapid development and climate change are escalating the rates of species loss, according to a May United Nations report. (AP Photo/Robert F. Bukaty)
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Number of monarch butterflies wintering in Mexico drops 22%
Carolyn Kaster
A fresh monarch butterfly wing is seen soon after it emerged in Washington, Sunday, June 2, 2019. Farming and other human development have eradicated state-size swaths of its native milkweed habitat, cutting the butterfly's numbers by 90% over the last two decades. It is now under considered for listing under the Endangered Species Act. (AP Photo/Carolyn Kaster)
Carolyn Kaster
A fresh monarch butterfly wing is seen soon after it emerged in Washington, Sunday, June 2, 2019. Farming and other human development have eradicated state-size swaths of its native milkweed habitat, cutting the butterfly's numbers by 90% over the last two decades. It is now under considered for listing under the Endangered Species Act. (AP Photo/Carolyn Kaster)
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Number of monarch butterflies wintering in Mexico drops 22%
Carolyn Kaster
A fresh monarch butterfly wing is seen soon after it emerged in Washington, Sunday, June 2, 2019. Farming and other human development have eradicated state-size swaths of its native milkweed habitat, cutting the butterfly's numbers by 90% over the last two decades. It is now under considered for listing under the Endangered Species Act. (AP Photo/Carolyn Kaster)
Carolyn Kaster
A fresh monarch butterfly wing is seen soon after it emerged in Washington, Sunday, June 2, 2019. Farming and other human development have eradicated state-size swaths of its native milkweed habitat, cutting the butterfly's numbers by 90% over the last two decades. It is now under considered for listing under the Endangered Species Act. (AP Photo/Carolyn Kaster)
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Number of monarch butterflies wintering in Mexico drops 22%
Carolyn Kaster
The monarch butterfly wing pattern is seen though its transparent chrysalis in Washington, Sunday, June 2, 2019. (AP Photo/Carolyn Kaster)
Carolyn Kaster
The monarch butterfly wing pattern is seen though its transparent chrysalis in Washington, Sunday, June 2, 2019. (AP Photo/Carolyn Kaster)
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Number of monarch butterflies wintering in Mexico drops 22%
Carolyn Kaster
Laura Moore displays a newly emerged monarch butterfly on her finger in her Greenbelt, Md., yard, Friday, May 31, 2019. Despite efforts by Moore and countless other volunteers and organizations across the United States to grow milkweed, nurture caterpillars, and tag and count monarchs on the insects' annual migrations up and down America, the butterfly is in trouble. (AP Photo/Carolyn Kaster)
Carolyn Kaster
Laura Moore displays a newly emerged monarch butterfly on her finger in her Greenbelt, Md., yard, Friday, May 31, 2019. Despite efforts by Moore and countless other volunteers and organizations across the United States to grow milkweed, nurture caterpillars, and tag and count monarchs on the insects' annual migrations up and down America, the butterfly is in trouble. (AP Photo/Carolyn Kaster)
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Number of monarch butterflies wintering in Mexico drops 22%
Carolyn Kaster
This photo shows a monarch butterfly after it emerged in Washington, Sunday, June 2, 2019. (AP Photo/Carolyn Kaster)
Carolyn Kaster
This photo shows a monarch butterfly after it emerged in Washington, Sunday, June 2, 2019. (AP Photo/Carolyn Kaster)
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Number of monarch butterflies wintering in Mexico drops 22%
Ann Heisenfelt
A Monarch butterfly eats nectar from a swamp milkweed on the shore of Rock Lake in Pequot Lakes, Minn., Sunday, July 22, 2012. (AP Photo/Ann Heisenfelt)
Ann Heisenfelt
A Monarch butterfly eats nectar from a swamp milkweed on the shore of Rock Lake in Pequot Lakes, Minn., Sunday, July 22, 2012. (AP Photo/Ann Heisenfelt)
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Number of monarch butterflies wintering in Mexico drops 22%
Marco Ugarte
A couple of Monarch butterflies mate at the Monarch Butterfly Biosphere Reserve, near the town of Chincua, Mexico, Thursday, Feb. 26, 2009. The Monarchs are not endangered, but scientists say deforestation could threaten its existence. (AP Photo / Marco Ugarte)
Marco Ugarte
A couple of Monarch butterflies mate at the Monarch Butterfly Biosphere Reserve, near the town of Chincua, Mexico, Thursday, Feb. 26, 2009. The Monarchs are not endangered, but scientists say deforestation could threaten its existence. (AP Photo / Marco Ugarte)
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Number of monarch butterflies wintering in Mexico drops 22%
Rebecca Blackwell
In this Jan. 4, 2015 photo, a swarm of Monarch butterflies fly between trees, in the Piedra Herrada sanctuary, near Valle de Bravo, Mexico. The population of the butterfly, that migrates thousands of miles each year from winter nesting grounds in Mexico, has been shrinking partly because farmers are growing more herbicide-resistant crops that have stripped millions of acres of milkweed they depend on to nourish them along their route. (AP Photo/Rebecca Blackwell)
Rebecca Blackwell
In this Jan. 4, 2015 photo, a swarm of Monarch butterflies fly between trees, in the Piedra Herrada sanctuary, near Valle de Bravo, Mexico. The population of the butterfly, that migrates thousands of miles each year from winter nesting grounds in Mexico, has been shrinking partly because farmers are growing more herbicide-resistant crops that have stripped millions of acres of milkweed they depend on to nourish them along their route. (AP Photo/Rebecca Blackwell)
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Number of monarch butterflies wintering in Mexico drops 22%
Marco Ugarte
Monarch butterflies fly in the Amanalco de Becerra sanctuary, on the mountains near the extinct Nevado de Toluca volcano, in Mexico, Thursday, Feb. 14, 2019. The Monarch butterflies arrive in central Mexico usually around the first week of November, after their yearly 4000-kilometer (some 2500 miles) migration from Canada and the United States, and begin their return around March. (AP Photo/ Marco Ugarte)
Marco Ugarte
Monarch butterflies fly in the Amanalco de Becerra sanctuary, on the mountains near the extinct Nevado de Toluca volcano, in Mexico, Thursday, Feb. 14, 2019. The Monarch butterflies arrive in central Mexico usually around the first week of November, after their yearly 4000-kilometer (some 2500 miles) migration from Canada and the United States, and begin their return around March. (AP Photo/ Marco Ugarte)
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Number of monarch butterflies wintering in Mexico drops 22%
Marco Ugarte
FILE - In this Feb. 14, 2019 file photo, a monarch butterfly rests on a man's forehead at the Amanalco de Becerra sanctuary, in the mountains near the extinct Nevado de Toluca volcano in Mexico. Tree loss in the wintering grounds of the monarch butterfly in central Mexico is down by about 25% in 2019 compared to last year as a sharp drop in Illegal logging more than made up from an increase in tree deaths due to lack of water or disease, experts said Monday, Oct. 28, 2019. (AP Photo /Marco Ugarte, File)
Marco Ugarte
FILE - In this Feb. 14, 2019 file photo, a monarch butterfly rests on a man's forehead at the Amanalco de Becerra sanctuary, in the mountains near the extinct Nevado de Toluca volcano in Mexico. Tree loss in the wintering grounds of the monarch butterfly in central Mexico is down by about 25% in 2019 compared to last year as a sharp drop in Illegal logging more than made up from an increase in tree deaths due to lack of water or disease, experts said Monday, Oct. 28, 2019. (AP Photo /Marco Ugarte, File)
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Number of monarch butterflies wintering in Mexico drops 22%
Rebecca Blackwell
Monarch butterflies cling to branches in their winter nesting grounds in El Rosario Sanctuary, near Ocampo, Michoacan state, Mexico, Friday, Jan. 31, 2020. (AP Photo/Rebecca Blackwell)
Rebecca Blackwell
Monarch butterflies cling to branches in their winter nesting grounds in El Rosario Sanctuary, near Ocampo, Michoacan state, Mexico, Friday, Jan. 31, 2020. (AP Photo/Rebecca Blackwell)
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Number of monarch butterflies wintering in Mexico drops 22%
Wilfredo Lee
FILE - In this July 1, 2019, file photo, a monarch butterfly lands on a penta plant in the front yard of Tom Carroll and Hermine Ricketts in Miami Shores, Fla. Homeowners can attract butterflies to their gardens with a multitude of plants that include fennel, dill, and milkweed. (AP Photo/Wilfredo Lee, File)
Wilfredo Lee
FILE - In this July 1, 2019, file photo, a monarch butterfly lands on a penta plant in the front yard of Tom Carroll and Hermine Ricketts in Miami Shores, Fla. Homeowners can attract butterflies to their gardens with a multitude of plants that include fennel, dill, and milkweed. (AP Photo/Wilfredo Lee, File)
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Number of monarch butterflies wintering in Mexico drops 22%
Gene J. Puskar
A Monarch butterfly pauses in a field of Goldenrod at the Flight 93 National Memorial in Shanksville, Pa., Friday, Sept. 11, 2020. (AP Photo/Gene J. Puskar)
Gene J. Puskar
A Monarch butterfly pauses in a field of Goldenrod at the Flight 93 National Memorial in Shanksville, Pa., Friday, Sept. 11, 2020. (AP Photo/Gene J. Puskar)