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Monarch Butterflies Making Trek North From Mexico in Lowest Numbers in Decades
 Bill Hanna - Star-Telegram
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March 19, 2010
Monarch butterflies, hit hard by strong storms at their winter home in Mexico, have dwindled to their lowest population levels in decades as they begin to return to Texas on their springtime flight back to the United States and Canada.
The monarch loss is estimated at 50 to 60 percent and means that the breeding population flying northward 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 percent. We've never seen it this bad before."
The butterfly colonies in the Mexican state of Michoacan were hit by torrential rainfall and mudslides in early February that also killed at least 40 people and left thousands homeless. Several towns were devastated by flooding.
Researchers put the butterfly population in Mexico at 1.92 hectares, down from the average of 7.44 hectares. The hectare count represents the areas with trees that contain monarchs. 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 public awareness campaign to encourage gardeners, farmers and transportation officials to plant milkweed. The plant is a lifeline for monarchs as they travel.
"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."
Milkweed feast
One bit of good news is that a wet fall and winter across Texas should help provide plenty of food to aid the monarchs' recovery. Gardeners without milkweed now probably don't have time to help this spring, but they can provide a big boost this fall.
The Fort Worth Botanic Garden collects seeds from native milkweed to distribute to interested gardeners during its annual fall plant sale.
During the fall migration, the butterflies obtain up to 70 percent of the food they need to survive the Mexican winter while flying through Texas and feasting on milkweed and other nectar producers, said Gail Manning, an entomologist with the Botanic Garden.
The generation of monarchs that makes the lengthy fall migration to Mexico and starts back to the United States the next spring can live as long as eight or nine months. Other generations can live for as little as three weeks; it can take three generations to make the northward trek across the U.S. during the spring and summer, Manning said.
Normally, butterflies headed north start appearing in North Texas between now and the end of March, Manning said. But they often pass through without being noticed because their numbers are so small.
Monarchs that appear later in the spring likely hatched from eggs here. Some will fly northward, while a small native population will remain in Texas throughout the summer.
Long recovery
There have already been sightings this week as far north as Austin and San Antonio, according to the Web site Journey North.
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. There is more stress on the butterflies because of habitat loss in the U.S. and Mexico, 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."
One Texan who traveled to Mexico after the storms said the monarch population was definitely smaller than in previous years, but he couldn't predict how quickly the butterflies will recover.
"It depends much on unknown factors: temperatures and moisture in the breeding zones, and the consequent conditions of their food plant," said Bill Calvert of Texas Monarch Watch. "It also depends on the population levels of their parasites and predators -- too many unknowns to predict with any certainty."
billhanna(at)star-telegram.com |
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