Monarch butterflies return to Mexico on annual migration

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

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

The monarchs have appeared a few days late this year. Usually they arrive for the Day of the Dead on November 1st and 2nd. Mountain communities have long associated the orange-and-black butterflies with the returning souls of the dead.

The department said the butterflies were seen around their three main 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 say how large this year’s annual migration from the US and Canada will be. The counts are usually made in January, when the butterflies have settled in clumps on spruce and pine branches.

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

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

Each year, generally in March, the monarchs migrate back to the United States and Canada.

Drought, severe weather and habitat loss north of the border – particularly of the milkweed plant 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 and loss of tree cover due to disease, drought and storms plague the reserves in Mexico.

This year, the International Union for the Conservation of Nature added the migrating monarch butterfly to its “red list” of endangered species, categorizing it as “threatened” – two steps from extinction.

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

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

After wintering in Mexico, the butterflies fly north, breeding for several generations along the way for thousands of kilometers. The offspring that reach southern Canada begin the journey back to Mexico in late summer.

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