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monarch butterfly Millions of monarchs have arrived for the winter.

Monarch numbers up but not enough

The butterfly migration is the second-lowest in 21 years

The monarch butterflies have been counted and the numbers are in: they’re up 69% from last year.

However, that’s still the second-lowest number in 21 years.

The butterflies migrate annually from Canada and the United States — a journey of up to 4,000 kilometers — to spend the winter in the forests of Michoacán and the State of México. But their numbers have been declining.

Last year they covered an area of 0.67 hectares, the lowest since monitoring began in 1993. This year that figure is up to 1.13 hectares. Butterfly numbers are measured in terms of the area they cover — made simpler by the fact that they cluster together on trees. The largest area ever recorded was considerably higher at 18.2 hectares in 1996-97.

An entomologist at Sweet Briar College in Virginia says anything less than two hectares means the butterflies are in danger. Lincoln Brower said four or five hectares would be “a sign of significant recovery.”

The decline in numbers has been attributed to destruction of habitat through illegal logging in Mexico, and the loss of milkweed, their main source of food, in the United States. The logging has been brought under control and efforts are under way in the U.S. to restore milkweed.

But worries remain about the monarch’s future: the U.S Fish and Wildlife Service is investigating whether the butterfly should be classified as endangered.

This year’s migration has brought nine colonies of monarch butterflies, three in Michoacán and six in the State of México. Five of those are inside the Monarch Butterfly Biosphere Reserve. The largest colony covers 0.57 hectares, about half the total, and is located in the ejido, or communal village, of El Rosario.

Visiting the reserve, where ejido residents offer guide services, is popular at this time of the year.

One guide, 73-year-old Audelia at the Sierra Chincua sanctuary in Michoacán, remembers that years ago the butterflies were considered an infestation and there were fears they would dry out the forest.

Sources: La Jornada (sp), El Universal (sp), AP (en)

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