VOA慢速英语2021--帝王蝶种群即将灭绝（在线收听）

The Monarch Butterfly Population Is in Danger of Disappearing

The warm coast of California is a place where many western monarch butterflies stay during the cold winter months in the United States. Researchers fear the record low number of monarchs this year could mean the insects are in danger of disappearing in the near future.

Researchers from the Xerces Society said they found fewer than 2,000 orange-and-black butterflies in the yearly count this January. That number showed a big drop from the tens of thousands in recent years. In the 1980s, there were millions of them in trees from Northern California's Marin County to San Diego County near the Mexico border.

Every winter, western monarch butterflies fly south from the northwestern U.S. to California, going to the same places and even the same trees. They often stay together to keep warm. At the start of November, they usually arrive in California. The insects then spread across the country once warmer weather arrives in March.

On the eastern side of the Rocky Mountains, another monarch butterfly population travels from southern Canada and the northeastern United States to spend the winter in Mexico.

Scientists estimate the eastern monarch population has decreased by 80 percent since the mid-1990s. But the decrease in the western monarch population has been much greater.

The Xerces Society works on conservation efforts for insects. Last winter, it recorded around 29,000 butterflies in its yearly survey. That was similar to the winter before, when an all-time low of 27,000 monarchs was counted.

But the count this year is dangerously low. Pacific Grove is a city known for having monarch butterflies during the cold season. But volunteers did not see a single one this winter. Other well-known areas, such as Pismo State Beach, Monarch Butterfly Grove and Natural Bridges State Park, only had a few hundred butterflies, researchers said.

Scientists say there are several causes for the extremely low numbers of butterflies in the western states.

Homebuilding and chemical use have destroyed milkweed plants along their migratory path. The plants are needed for monarch butterflies to grow and develop. Climate change interferes with the growth of wild plants. And huge wildfires in the west may also have influenced their migration.

A 2017 Washington State University study predicted that monarch butterflies would likely disappear within 10 to 20 years if the population dropped below 30,000 and nothing was done to save them.

Last December, U.S. federal officials said the monarch butterfly is "a candidate" for the threatened or endangered species list. The designation would provide protection for their food supply and environment, including their migratory path. However, they said no action would be taken for several years because many other species are still awaiting that designation.

The Xerces Society said it will keep working with other partners to protect the monarch. The organization added that people can help by planting flowers and milkweed along these butterflies' migratory path.

Words in This Story

conservation – n. the protection of animals, plants, and natural resources

milkweed – n. type of North American plant that has white juice

migratory – adj. moving from one place to another at different times of the year

endangered – adj. used to describe a type of animal or plant that has become very rare and that could die out completely

species – n. a particular group of things or people that belong together