NPR:
“Monarch butterflies are disappearing. Populations of these distinctive black and orange migratory insects have been in precipitous decline for the past 20 years, but scientists aren’t exactly sure what’s causing them to vanish.
So far, potential culprits include disease, climate change, drought and deforestation. Everyone from loggers to suburban developers has been implicated. But much of the blame has been placed on farmers and the pesticides they rely on — pesticides that have reduced the milkweed that monarch caterpillars feast on. Now, however, scientists say that may not be the full story.
Every spring, hundreds of thousands of monarchs sweep across the Great Plains from Mexico to Canada, and then back again in the fall. It’s an amazing journey, one that takes place over multiple generations for the butterflies. The insects breed while traveling north, expending four generations to make it to Canada. The final generation then flies all the way back to Mexico to spend the winter there.
Monarch populations are measured in hectares (roughly 2 1/2 acres). Surveys of their wintering habitats in the central mountains of Mexico show dense populations of monarchs at an average of more than nine hectares during the winters from 1995 to 2002. In 2014, monarchs took up less than one hectare.”
