…once a familiar sight, are plummeting toward extinction due to landscape-scale threats from pesticides, development and climate change. That's why the Center [for Biological Diversity] is working hard to win them protection under the U.S. Endangered Species Act.
Monarchs have declined 85% in two decades. The western population — which overwinters in California as part of its international migration — has suffered a heartbreaking 99% decline. Overall the migrating populations are less than half the size they need to be to avoid extinction.
Monarchs are threatened by pesticides — including toxic neonicotinoids and herbicides, which are killing off the milkweed plants they need to survive — as well as urban development and climate change.
*source: Center for Biological Diversity