In the 1980s, the monarch butterfly population was nearly 4.5 million. However, their numbers have decreased by 99.4 percent since then, which means that for every 160 monarch butterflies in the 1980, there is only one left today, according to a report by Willamette Week.

Xerces Society for Invertebrate Conservation recently conducted a survey and showed the black-and-orange pollinators are facing an “irreversible extinction.”

Monarch butterflies are known to travel thousands of miles across the world on an annual basis and pollinate a lot of wildflowers. According to Willamette Week, they are also the only known migratory butterfly who travel at the Western seaboard and roost in places like Santa Cruz and San Diego during the winter season.

Scientists believed that the sudden decline of the monarch butterflies could be rooted from the radioactive fallout in the mid-20th century and when nuclear weapon testing began all across the globe, which had serious impacts on the environment and all lives.

“We’ve been whittling away at some of these populations for a while as we lose habitat with climate change and with pesticides,” Emma Pelton, conservation biologist and lead researcher of the study at Xerces, said in a statement.

Xerces Society is petitioning legislators in California to implement stricter rules to protect the butterflies’ breeding sites and for all residents to create more pollinator-friendly places.

“They’re huge keystone part of the ecosystem,” Pelton said. “If we lose them, we’re going to lose more than I think we can imagine right now.”