MEXICO CITY ( Associated Press) — Mexican experts reported Monday that the number of monarch butterflies that arrived this year to spend the winter in mountain forests increased by 35% compared to the previous season.
The increase, according to experts, could reflect the ability of butterflies to adapt to more extreme episodes of heat or drought, by changing the date they leave Mexico.
Mexico’s National Commission for Natural Protected Areas (CONANP) noted that the butterfly population covered 2.84 hectares (7 acres) this year, compared to 2.1 hectares (5.2 acres) in 2021.
The annual butterfly count does not calculate the number of individual butterflies, but the amount of hectares they cover when they are grouped on the branches of trees.
Each year, monarch butterflies return to the United States and Canada as part of an annual migration that has been threatened by the loss of milkweed they feed on in the north and deforestation in butterfly reserves in Mexico.
Gloria Tavera, regional director of CONANP, said logging in the butterflies’ hibernation zone increased 4.5% this year, to 13.9 hectares (34 acres).
However, fewer trees were lost to fire, drought, or plant diseases and pests. Total tree loss in the 2021-22 season was about 18.8 hectares (46 acres), up from 20.6 hectares (51 acres) in the 2020-21 season.
But environmentalist and writer Homero Aridjis, who grew up near the reserve, said “there are no reliable data on the full extent of timber extraction from the reserve,” noting that loggers often take undamaged trees, claiming that they were sick or had been affected by storms.
The butterflies usually arrive in early November in the pine and fir forests of the mountains west of Mexico City. They normally leave for the United States and Canada in March.
But Tavera said last year was unusual in that the butterflies began their return journey in February, allowing them to leave before drought and heat hit north of the border in April and May.
“They are starting to adapt to extreme weather conditions,” Tavera said.
Strangely, this year, the butterflies stayed in Mexico longer than usual. “They left very late. We still had butterflies in April,” said Tavera. Whether that strategy worked for them remains to be seen in next year’s numbers.
Although activists and students in the United States and Canada have been urged to plant milkweed to compensate for the loss of the plant due to clearing of land for farming and grazing and the use of herbicides, that strategy has backfired in Mexico.
Tavera urged Mexicans not to plant milkweed in Mexico, saying it could affect migration by encouraging monarchs to stay in the country, rather than head north. He also urged people not to breed monarchs in captivity – they are sometimes released at weddings or other celebrations – saying that could spread diseases among the insects.
Jorge Rickards of the environmental group WWF pointed out that, despite this year’s increase, “this continues to be a migratory phenomenon at risk.”
A positive point was that more than 160,000 tourists visited the butterfly reserves in Mexico in 2021, an increase of 132% compared to the number of people who visited the reserve during the coronavirus pandemic in 2020.
Local farming groups that own much of the reserve’s forests rely on tourism for income and discourage logging.
Drought, extreme weather conditions and habitat loss – especially of the milkweed where monarchs lay their eggs – as well as the use of pesticides and herbicides, and climate change, pose threats to the species’ migration. Illegal logging and loss of tree cover due to disease, drought and storms also continue to affect reserves.
But Aridjis said the reserves also suffer from pressure from drug cartels and the illegal planting of avocado orchards, which thrive in the same general climate as pine forests.
“There is drug trafficking, and bodies regularly appear on remote roads,” Aridjis said of the area around his hometown of Contepec. “I feel like an exile from my birthplace.”