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For the second straight year, the number of monarch butterflies arriving in Mexico for their winter retreat has dropped dramatically, according to Mexican government sources.

Compared to last year, the number of monarchs, which migrate annually from as far north as Canada during the winter months, has dropped by nearly 15 percent compared to last year’s figures, covering only 2.48 hectares of oyamel forests in Michoacán and the State of Mexico, down from 2.91 hectares in the 2016-2017 season, according to Alejandro del Mazo, the country’s commissioner for protected areas.

One possible cause of the drop in the butterflies’ numbers was, according to the World Wildlife Fund, a particularly brutal hurricane season across the monarchs’ migration route.

Also, unrestrained logging practices and the untethered use of pesticides in the orange and black butterflies’ winter resting ground continue to threaten the fragile ecosystem in the area.

Each autumn, more than 100 million monarchs traditionally arrive in Mexico from the United States and Canada, traveling as far as 5,000 kilometers to reach their winter home, where they usually stay through early March.

The monarchs always travel in colonies of about 10 to 20 million and follow the same migrating patterns year after year.

Although little is actually known about how the butterflies’ migration is programmed, scientists currently believe that they somehow guide themselves by sensing variations in the earth’s magnetic field.

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