More Monarch Butterflies Than Usual Appear to Be Migrating This Fall

Andrea Beck

Every autumn, monarch butterflies migrate across the U.S., heading south (and in some cases, west) for the winter. They are one of the few butterfly species that makes such a long migration—it can be up to 3,000 miles, and they often travel in such large groups that they fill the sky with their orange-and-black wings and blanket vegetation when resting. But over the past two decades, their numbers have been steadily declining, to the point that this insect is being considered for the endangered species list. Since 1997, when an estimated 682 million monarchs swooped through the air, the population has dwindled as low as 25 million monarchs in 2014 before rebounding to 150 million in 2016. So when reports of this year’s migration seem to indicate more of these winged wonders than usual, it could be a sign that their populations are continuing to make a comeback.

Courtesy of Monarch Watch

In North America, two separate monarch populations migrate every fall. For the eastern population of butterflies, their migration typically begins in the northeastern U.S. and Canada where they live for the summer. They then travel south throughout the country, passing through most states in the U.S. on their way to spend the winter in Mexico. But monarchs that live west of the Rocky Mountains head to California for the winter, traveling there from states like Nevada and Utah, and south from Washington and Oregon. In spring, each of these populations reverses its route to migrate northward for the summer.

This year, observers along the eastern migration route have reported seeing larger numbers of butterflies than usual headed south for the winter. At the beginning of October, hundreds of butterflies were even caught on video by Colorado Parks & Wildlife near Lamar, Colorado. The video shows a huge group of monarch butterflies resting on trees and bushes, with dozens more in the sky. And on October 16, the Lady Bird Johnson Wildlife Center reported that the monarchs had made it to Austin, Texas, and reiterated that the group seemed larger than usual.

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Data from earlier in 2019 could also support anecdotal evidence of a larger migration this fall. Back in January, the Center for Biological Diversity reported that the population spending the winter in Mexico had increased by 144% since counts were taken in early 2018. The count taken in January 2019 showed the highest number of monarchs at the overwintering site since 2006. Additionally, the weather’s been good for monarchs this year. Journey North, a citizen science program that monitors all sorts of migrating animals, noted that the temperature and rainfall have both been favorable for increased egg and larvae survival, meaning more butterflies could make it to adulthood and reproduce.

All of this is very good news for monarchs, but it’s still too early to say if this year’s migration truly comprises a larger number of butterflies than usual. Matthew Shepard, the director of communications and outreach for the Xerces Society for Invertebrate Conservation points out that the only time researchers can get an accurate population count is while the monarchs are clustered together at overwintering sites in Mexico and California. “At this point in the year, we won’t know how monarchs are doing in either the eastern states or the west,” Shepard says. “While monarchs are spread across the landscape, it isn’t possible to get an overall count, only a sense of how things are based on the number passing through a few scattered locations.”

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It's also worth noting that even if the final count shows an increased number of monarchs in their winter locations, that may not mean the species as a whole is out of danger from extinction. Overall monarch populations naturally tend to fluctuate in both the east and west, depending on weather and other factors that could result in lower numbers next year. But the western monarch population, in particular, has a long way to go. According to the Center for Biological Diversity, it dropped to less than 30,000 at the beginning of 2019, down from 1.2 million 20 years ago.

Still, the possibility that monarch populations may be modestly rebounding is exciting, especially given all the nationwide efforts to help these butterflies. Multiple conservation groups, like the Xerces Society, Monarch Watch, and the Monarch Joint Venture, have been working hard to stop the decline in monarch populations across North America. If this year’s migration does turn out to be larger than usual, it could be a sign that their efforts are starting to pay off.

Blaine Moats

In addition to supporting organizations like these and participating in citizen science projects focused on monarchs, one of the most effective ways to help these butterflies increase their numbers is through gardening. Start by growing some milkweed, which is the only plant that monarchs will lay their eggs on, and the only food the resulting caterpillars will eat. And make sure you have lots of other nectar-rich flowers to feed the adults, such as lantana, verbena, and yarrow. Pesticides have also contributed to the declining monarch population (butterflies are especially susceptible to these chemicals), so avoid using them as much as possible. Taking these steps will not only make your garden a more pleasant place for you, it will make it much more inviting for monarch butterflies to visit. It might even become a monarch destination during the next migration!