USA Today reported that the species has dropped by around 97% since the 1980s.
Every year, according to USA Today, monarch butterflies in the western U.S. migrate from inland areas to California’s coastline to spend the winter. This year, Emma Pelton, a conservation biologist with the Xerces society (named for an extinct California butterfly, according to their website), told USA Today that “It’s been the worst year we’ve ever seen.”
Pelton told USA Today that the cause of the dropoff is multifactorial; late rainy-season storms across California last month, the drought, the wildfires, pesticide use and hotter weather brought about by climate change all may play a role.
USA Today also reported, however, that the eastern monarch population seems to be doing well this year, although their numbers have also declined by around 80% since the mid-1990s.