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Experts: Monarch butterfly population in jeopardy

By Sameera Gokal

Monarch butterflies flock annually to the mountains of central Mexico in winter and head back north in spring.
Monarch butterfly
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Sweet Briar College

ATLANTA, Georgia (CNN) -- Monarchs are dying in Mexico. No, not kings and queens, but creatures that are just as majestic -- in the butterfly world.

Monarch butterflies flock by the millions to the tree-laden mountains of central Mexico each November and depart for northern climes the first of April.

On their return northward, the monarchs lay their eggs on milkweed plants and die, according to the Encyclopedia Britannica. The eggs hatch and mature, and a new generation continues the trip. Each group is three to five generations removed from the previous arrivals.

In recent years, bitter cold, severe rainstorms and droughts have taken their toll on the delicate creatures. Experts say that three of the past five winters in Mexico have seen major die-offs in monarch populations.

Additional threats, say researchers, include loss of habitat and a declining food supply due to the rise in illegal logging operations and the unrestricted spraying of pesticides and other poisons in forested areas of Mexico where the butterflies are known to gather.

Although the butterflies showed signs of rebound in 2003, hundreds of millions of monarchs succumbed over the past two years to winter temperatures in Mexico that were the coldest in a decade, scientists say.

"In 2002 and January 2004, there were severe winter storms from Canada to Mexico, and because of the high altitude, millions of monarch butterflies froze to death," says Lincoln Brower, a biologist at Sweet Briar College in Virginia. "They were killed last winter, and many did not get back to the United States for the spring."

Brower, an expert on monarch butterflies, says that the 2004 migration was the lowest he has ever seen.

Other experts acknowledge that the number of monarch butterflies is down by as much as 75 percent, and the birth of this season's migration again has signaled the death of millions of butterflies.

Researchers have spent years trying to decipher the reasons for the butterflies' annual migration from Canada to Mexico. The practice has been linked to a variety of factors, including internal clocks and instinct.

With their orange and black coloring and wing pattern, monarchs are one of the largest butterflies in North America and the best-known species.

Despite their size, the butterflies remain vulnerable to cool climatic conditions and rely on clustering in large numbers and the safety of forests to keep warm.

"In 2004, there was not a good recovery because of the low spring population, the summer being extremely cold, and the loss of habitat in the upper Midwest," says Chip Taylor, a professor at the University of Kansas.

Scientists say they fear the migration situation could worsen as butterflies and forests in Mexico continue to decline.

They say the loss of habitat means monarchs will produce fewer offspring and migrating numbers will be the lowest in the past 14 years.

"If we lose the whole migration, we lose one of the nation's most magnificent phenomenon." Taylor says. "They are pollinators of native plants and have impacts on plants utilized.

"These butterflies are the symbol of richness of biological diversity and marvelous scientific aspect."

CNN's Camille Feanny contributed to this report.

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