Monarch butterflies drop, migration may disappear

http://apnews.myway.com/article/20140129/DABKNK580.html

Jan 29, 5:00 PM (ET)
By MARK STEVENSON

MEXICO CITY (AP) - The stunning and little-understood annual migration of millions of Monarch butterflies to spend the winter in Mexico is in danger of disappearing, experts said Wednesday, after numbers dropped to their lowest level since record-keeping began in 1993.

Their report blamed the displacement of the milkweed the species feeds on by genetically modified crops and urban sprawl in the United States, extreme weather trends and the dramatic reduction of the butterflies' habitat in Mexico due to illegal logging of the trees they depend on for shelter.

After steep and steady declines in the previous three years, the black-and-orange butterflies now cover only 1.65 acres (0.67 hectares) in the pine and fir forests west of Mexico City, compared to 2.93 acres (1.19 hectares) last year, said the report released by the World Wildlife Fund, Mexico's Environment Department and the Natural Protected Areas Commission. They covered more than 44.5 acres (18 hectares) at their recorded peak in 1996.

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While the Monarch is not in danger of [immediate] extinction, the decline in their population now marks a statistical long-term trend and can no longer be seen as a combination of yearly or seasonal events, experts said.

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"The main culprit," he wrote in an email, is now genetically modified "herbicide-resistant corn and soybean crops and herbicides in the USA," which "leads to the wholesale killing of the monarch's principal food plant, common milkweed."

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Extreme weather - severe cold snaps, unusually heavy rains or droughts in all three countries - have also apparently played a role in the decline.

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Oberhauser noted that some Monarchs now appear to be wintering along the U.S. Gulf coast, and there has been a movement in the United States among gardeners and home owners to plant milkweed to replace some of the lost habitat. But activists say large stands of milkweed are needed along the migratory route, comparable to what once grew there. They also want local authorities in the U.S. and Canada to alter mowing schedules in parks and public spaces, to avoid cutting down milkweed during breeding seasons.

The migration is an inherited trait. No butterfly lives to make the full round-trip, and it is unclear how they remember the route back to the same patch of forest each year, a journey of thousands of miles to a forest reserve that covers 193,000 acres (56,259-hectares) in central Mexico. Some scientists think the huge masses of migrating butterflies may release chemicals that mark the migratory path and that if their numbers fall low enough, not enough chemical traces would remain and the route-marking might no longer work.

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Butterfly guide Emilio Velazquez Moreno, 39, and other farmers in the village of Macheros, located inside the reserve, have been planting small plots of milkweed in a bid to provide food for the Monarchs if they decide to stay in Mexico year-round, which he said some do.

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