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Monarch butterflies suffer population loss

Storms in Mexico devastate an already low population of the migrating butterfly. An advocacy group encourages landowners to plant milkweed to help the survivors travel.

March 20, 2010|By Bill Hanna

Reporting from Fort Worth, Texas — Monarch butterflies, devastated by storms at their winter home in Mexico, have dwindled to their lowest population levels in decades as they begin to return to the United States and Canada.

The monarch loss is estimated at 50% to 60%, which means the breeding population is expected to be the smallest since the Mexican overwintering colonies were discovered in 1975, said Chip Taylor, a professor of entomology and director of Monarch Watch at the University of Kansas.

"I think it is very clear that the butterflies lost more than half of the population," Taylor said. "I'm hoping it wasn't as high as 70% or 80%. We've never seen it this bad before."

The butterfly colonies in the Mexican state of Michoacan were hit by torrential rain and mudslides in early February that killed at least 40 people and left thousands homeless. Several towns were devastated by flooding.

Researchers put the butterfly population in Mexico -- measured in hectares, which represent the areas with trees that contain monarchs -- at 1.92 hectares, down from the average of 7.44. There is no consensus on how many monarchs can be in a hectare, but researchers say the number may be as high as 50 million.

The monarch population was already unusually low because of unfavorable conditions in parts of the U.S. and Canada last summer.

As a result, Monarch Watch is starting a campaign to encourage gardeners, farmers and transportation officials to plant milkweed, a monarch favorite. The plant is a lifeline for the traveling butterflies.

"It's not just the backyard garden," Taylor said. "We're hoping to encourage changes in roadside management practices, how public lands are managed and how people are managing what they would call nonproductive land or marginal land that they might own."

It will take several years at least for the monarchs to recover from their losses. And researchers are still trying to understand these sudden drops. Habitat loss in the U.S. and Mexico puts more stress on the butterflies, but that may not completely explain the dramatic population swings.

"Is there a cycle to the population?" Manning said. "Is it normal to have a crash and then a rebuilding process? We're still not sure if it is an abnormality to have these crashes or something nature has coped with for years."

Hanna writes for the Fort Worth Star-Telegram.

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