It’s hard to know what to make of the recent monarch butterfly news. On one hand, the western population of monarchs native to California is down 86 percent this year compared to last – reaching a dangerously low threshold that puts them on the brink of extinction. On the other hand, the eastern population that migrates east of the Rockies and overwinters in Mexico is up 144 percent – the highest count since 2006.
With the U.S. Fish and Wildlife Service currently weighing the need to list monarch butterflies as threatened or endangered, the stakes are incredibly high to understand what these population trends mean for the iconic species.
So how do scientists explain these apparently conflicting population numbers?