Hundreds of monarch butterflies line a tree trunk in the El Rosario butterfly sanctuary in Mexico. (Photo: Andrew Winning/Reuters)

Each fall, millions of monarch butterflies take flight during their annual migration—a grueling almost 3,000-mile trek from Canada and the eastern United States to Mexico and southern California. This year, they'll have plenty of protected places to rest along the way.

Officials in Mexico, the United States, and Canada have named 13 wildlife preserves as safe havens for the orange and black butterflies, the U.S. Fish and Wildlife Service reported last week. The decision is a response to growing concerns about the safety of monarchs.

"The monarch population is under threat as Mexican loggers and American developers continue to devour its habitat," says Dr. Lincoln Brower, a biologist and monarch researcher at Sweet Briar College in Virginia. Because the agreement does not stop this logging or other practices harmful to monarchs, Brower added, it's only a first step in preserving their habitats.

According to Brower, illegal loggers have been cutting down trees in Mexico's Monarch Butterfly Reserve, while builders are demolishing California's eucalyptus groves. Both places are destinations for the migrating butterflies.

The use of pesticides in these regions is also threatening these butterflies. The application of weed killers is killing off the milkweed plant—the only plant monarch caterpillars eat.

"I think it's wonderful," Brower said about the three-country collaboration that aims to protect the monarch population. "It is important that the countries keep pressure on each other."

The Great Migration

Each fall, monarchs fly west to make their winter home in the fir forests of Mexico's Sierra Madre Mountains and the eucalyptus groves of southern California. The migration of monarchs is a sight that attracts many tourists.

In the spring, the butterflies fly back home, where they lay their eggs. Typically, a monarch will make one roundtrip in its lifetime.

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