MEXICO CITY (Reuters) - More than 27 percent fewer monarch butterflies migrated to Mexican forests during the 2016/2017 season, a study showed on Thursday, fueling concerns the orange-and-black insect could face growing threats from weather and deforestation.
During the second half of December 2016, monarch butterflies covered 2.91 hectares (7.2 acres) of fir and pine forests in the central states of Michoacan and Mexico, compared with 4.01 hectares (9.9 acres) in the same period in the previous year, the study said.
Led by the World Wildlife Fund, Mexico's National Commission of Natural Protected Areas (CONANP), and others, the study cited fewer mating sites, extreme weather and deforestation as threats to the migration of the monarch butterfly.
Monarch density in Mexico reached a record low during the 2013/2014 season, when the butterfly occupied just 0.67 hectares (1.6 acres) of the forests, the study noted.
While their numbers have rebounded in recent years since, they are still well below what they were two decades ago.
The butterflies congregate in Mexico and then go through several generations as they fly north on their long migration to Canada.
Their plight has become an international issue in the past. In February 2014, the United States, Mexico and Canada agreed to set up a joint task force to protect the butterflies.
Monarchs lay eggs only on milkweed plants, which grow wild throughout the United States. But milkweed, on which butterfly larvae feed, can cause stomach problems for cattle that eat it, so ranchers and farmers destroy the plant, researchers say.
Reporting by Natalie Schachar; Editing by Sandra Maler