Monarch butterflies (Danaus plexippus), which have been steeply declining throughout their range, showed a significant increase in their overwintering areas in Mexico, a World Wildlife Fund survey shows. The WWF completed an annual survey of the butterflies and found that monarch colonies have more than doubled the area they’re found in compared to last year. Researchers found 14 colonies, including eight within the monarch butterfly biosphere reserve. Monarch numbers in the wintering range have reached their highest point since 2006-2007, the WWF said, but are still much lower than they were 20 years ago. The improved numbers come as the U.S. Fish and Wildlife Service is deciding whether or not to list the species under the Endangered Species Act. It is expected to reach a decision in June.