Mexican experts said on Monday that 35 percent more monarch butterflies arrived this year to spend the winter in montane forests, compared to the previous season.
Experts say the rise may reflect the butterflies’ ability to adapt to more extreme periods of heat or drought by varying the date they leave Mexico.
The government commission on conservation areas said the butterfly population was 2.84 hectares this year, compared to 2.1 hectares last year.
The annual butterfly count does not calculate the individual number of butterflies, but rather the number of acres they cover when clumping together on tree branches.
Each year, the monarchs return to the United States and Canada for an annual migration threatened by the loss of the milkweed they feed on north of the border, and deforestation in Mexico.
Gloria Tavera, the regional director of Mexico’s Commission for National Protected Areas, said logging in the butterflies’ wintering grounds has increased by about 4.5 percent this year to 13.9 acres.
However, fewer trees were lost to fire, drought or plant diseases and pests. The total tree loss in the 2021-22 season was therefore 18.8 hectares, compared to 20.2 hectares in the 2020-21 season.
Adapt to the climate
The butterflies traditionally arrive in late October and early November in the pine and pine forests on the mountaintops west of Mexico City. They normally leave for the US and Canada in March.
But Tavera said last year was unusual, as the monarchs started to leave in February; allowing them to get out before drought and heat hit just north of the border in April and May.
“They’re starting to adapt to extreme climate conditions,” Tavera said.
Oddly enough, this year the butterflies lingered longer than usual in Mexico. “They left very late. In April we still had butterflies,” Tavera said.
Whether that strategy worked for them remains to be seen from next year’s figures.
While activists and students in the United States and Canada have been urged to plant milkweed to make up for losses from farmland and pasture clearing and herbicide use, that strategy has backfired in Mexico. .
Tavera urged Mexicans not to plant milkweed in Mexico, as it could disrupt migration by encouraging monarchs to stay, rather than move north. She also urged people not to breed monarchs in captivity — they are sometimes released at weddings or other celebrations — and said this could spread disease among the insects.
Jorge Rickards of the World Wildlife Fund’s environmental group said that despite the increase this year, “this is still a migratory phenomenon at risk.”
One bright spot was that more than 160,000 tourists visited Mexico’s butterfly sanctuaries in 2021, a 132 percent increase from the number visited during the coronavirus pandemic in 2020.
The local collective farm groups that own much of the forest in the reserves depend on tourism for income and to discourage logging.
The annual butterfly count is conducted in December every year. There are so many millions that the study is not counting the individual number of butterflies, but rather the number of acres they cover when they clump together on tree branches.
Drought, severe weather and loss of habitat – especially of the milkweed where the monarchs lay their eggs – as well as the use of pesticides and herbicides and climate change all threaten the migration of the species. Illegal logging and loss of tree cover from disease, drought and storms also continue to plague the reserves.