The number of monarch butterflies that overwintered in forests in Mexico fell for a second straight year, experts say.
Monday's count of 6.12 acres of winter habitat is down from the 7.19 acres last winter.
Monarch populations are measured by the number of acres of trees occupied by clustering butterflies that spend the winter in Mexico.
"The decrease is attributed to the presence of two tropical storms and three hurricanes that hit the Atlantic coasts in mid-September 2017 when migration begins," said Jorge Rickards, head of the World Wildlife Fund in Mexico. "This impacted the number of Monarchs that arrived in Mexico."
Unusually warm temperatures in the U.S. Midwest and Northeast also caused a late migration and resulted in low occupancy areas in Mexico, Rickards said.
In addition to bad weather, illegal logging and habitat destruction are the main threats to the butterflies, according to Rickards. "But how many monarch butterflies arrive to hibernate to the mountains of Mexico depend on how many can survive during their migration route in the United States, Canada and Mexico," he said.
Increased use of herbicides in the U.S. have hurt the prevalence of milkweed, which monarch caterpillars feed on, risking their survival, the Associated Press said.
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