2014-01-29. Migration of Monarch Butterflies Shrinks Again Under Inhospitable Conditions.

posted Feb 4, 2014, 11:37 AM by Alan Gould
For GSS Ecosystem Change chapter 4. Excerpt: Faltering under extreme weather and vanishing habitats, the yearly winter migration of monarch butterflies to a handful of forested Mexican mountains dwindled precipitously in December, continuing what scientists said was an increasingly alarming decline. ...Mexico is the southern terminus of an age-old journey in which monarchs shuttle back and forth between far-flung summertime havens in Canada and the United States and a single winter home in Mexico’s Sierra Madre mountains. ...The latest drop is best explained by a two-year stretch of bad weather, said Chip Taylor, a biologist at the University of Kansas.... But while good weather may help the monarchs rebuild their numbers, their long-term problem — the steady shrinking of habitat along their migratory route — poses a far greater danger. The monarchs’ migratory freeway runs through the Great Plains. As they flew north from Mexico in early 2012, Dr. Taylor said, months of near-record heat sapped their endurance and skewed their migratory patterns in ways that limited their ability to reproduce. Last spring, he said, the opposite happened: Unusual springtime cold in Texas delayed the butterflies’ northward migration, causing them to arrive late in areas where they would normally have bred weeks earlier. ...Monarchs lay their eggs only on milkweed, and patches of the plant have rapidly disappeared from the Great Plains over the last decade. As corn prices have risen — spurred in part by a government mandate to add ethanol to gasoline — farmers have planted tens of millions of acres of idle land along the monarchs’ path that once provided both milkweed and nectar. ...The monarchs are but the most visible victims of the habitat loss, Dr. Oberhauser said. A wide variety of pollinators and other insects, including many that are beneficial to farmers, are also disappearing, she said, along with the predators that feed on them.... http://www.nytimes.com/2014/01/30/us/monarch-butterflies-falter-under-extreme-weather.html. Michael Wines, The New York Times.