MEXICO CITY (March 13, 2013)—The number of Monarch butterflies wintering in Mexico dropped 59 percent this year, falling to the lowest level since comparable record-keeping began 20 years ago.
It was the third straight year of declines for the orange-and-black butterflies that migrate from the United States and Canada to spend the winter in mountaintop fir forests in central Mexico.
Drops have been reported in six of the last seven years and the count is one-fifteenth of what it was in 1997.
The millions of Monarchs cluster so densely on tree boughs that researchers don't actually count them individually, but instead measure the amount of forest they cover.
This winter, they covered just 2.93 acres, down from 7.14 acres last year.