Every November, volunteers with the Western Monarch Thanksgiving Count gather along the California coast to do just that – count butterflies. But this year, the citizen scientists noticed a dramatic difference from last year: the butterflies simply aren't showing up.
Now, the group’s hosting conservation society says that preliminary numbers suggest western monarchs have been reduced to less than 0.5 percent of their historic size, declining by 86 percent when compared with last year. Their findings are particularly dismal considering western monarch butterflies have already declined by 97 percent over the last two decades.
During the spring and summer months, western monarch butterflies breed across the western interior states -- from Washington, Idaho, Nevada, Utah, and a handful of other states – before migrating to the California coast to spend the colder winter months there. Citizen journalists throughout the western state counted butterflies at 97 sites, many of which are home to the most important overwintering populations. In 2017, these key sites hosted an estimated 148,000 monarchs. This year, numbers show just over 20,000. If the recent data shows the same trend then researchers anticipate less than 30,000 total butterflies will spend their winter in California, pushing the population dangerously low to collapsing.
Researchers aren’t sure why populations are dropping so drastically, but suspect mass mortality events could occur between the late overwintering season and early spring when adults are more exposed to the elements at the end of their life, thus making them more vulnerable. Weather could also be a factor, as California saw late-season rainstorms and a severe and extended wildfire season throughout much of the butterflies’ migratory grounds. Not to mention smoke and bad air quality that plagued the west paired with unprecedented drought conditions in the state.
A study published last year in Biological Conservation found that monarch populations in western North America are in sharp decline and in far greater danger of extinction than their eastern counterparts with a likelihood of 72 percent in 20 years and 86 percent in 50. According to a statement from the conservation group Xerces Society, some 10 million monarchs spent their winter in coastal California in the 1980s before experiencing sudden drops in 1997 and again in 1998.
“This study doesn’t just show that there are fewer monarchs now than 35 years ago. It also tells us that, if things stay the same, western monarchs probably won’t be around as we know them in another 35 years,” said Cheryl Schultz in a statement at the time.
Without substantial recovery efforts, conservation researchers say the future doesn’t look great. However, the team recommends a few simple solutions such as restoring native milkweed and other nectar plants that fuel the butterflies’ migrations and limiting pesticides in known butterfly habitat.