Monarch butterflies return to Mexico a few days late on their annual migration

MEXICO CITY (AP) — The first monarch butterflies have appeared in the highland forests of central Mexico where they spend the winter, Mexico’s environment department said Saturday.

The first butterflies have been seen exploring mountaintop reserves in the states of Mexico and Michoacan, apparently trying to decide where to settle this year.

The monarchs showed up a few days later this year. Normally they arrive for the Day of the Dead celebrations on November 1 and 2. Mountainside communities have long associated orange and black butterflies with the souls of the returning dead.

The department said the butterflies were seen around their three largest traditional wintering grounds – Sierra Chincua, El Rosario and Cerro Pelón in Michoacan state.

The main group of butterflies is expected to arrive in the coming weeks, depending on weather conditions, the department said in a statement.

It is too early to tell what the magnitude of annual migration from the United States and Canada will be this year. These counts are usually made in January, when the butterflies have settled in clumps on the branches of fir and pine trees.

The annual butterfly count does not calculate the number of individual butterflies, but rather the number of acres they cover when they group together.

Last year, 35% more monarch butterflies arrived than the previous season. The increase may reflect the butterflies’ ability to adapt to more extreme heat or drought events by varying the date they leave Mexico.

Each year, usually in March, monarchs return to the United States and Canada.

Drought, severe weather and habitat loss north of the border – particularly of milkweed where monarch butterflies lay their eggs – along with pesticide and herbicide use and climate change all pose threats to migration of the species. Illegal logging and loss of forest cover due to disease, drought and storms plague Mexico’s reserves.

This year, the International Union for Conservation of Nature added the migratory monarch butterfly to its “red list” of threatened species and classified it as “endangered” – one step away from extinction.

The group estimates that the monarch butterfly population in North America has declined between 22% and 72% over 10 years, depending on the method of measurement.

Monarch migration is the longest of any insect species known to science.

After overwintering in Mexico, the butterflies fly north, reproducing over several generations over thousands of miles. Offspring that reach southern Canada begin the return journey to Mexico in late summer.


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