When it comes to the 2019 monarch butterfly population, the numbers suggest catastrophe in California and a rebound in Mexico.
On the west coast, the news is dismal. The western population of monarch butterflies, which travel up and down the California coast, hit a historic low this year according to a study by the Xerces Society.
The California monarch population has dropped 86% since last year, according to the Xerces Society. Photo by Jenny Singleton
Xerces, a pollinator advocacy organization based in Portland, Oregon, has been monitoring the California monarchs for decades. In 1981, more than one million of the iconic orange and black insects were recorded overwintering in eucalyptus trees along the Pacific coast.
This year? The group’s most recent count over Thanksgiving weekend recorded less than 30,000 butterflies—an 86-percent decline since 2017 alone.
Emma Pelton, the Xerces biologist who oversaw the study, called the findings “potentially catastrophic” and a “wake-up call.”
Wildfires, deforestation, climate change, pesticide abuse, and poor land management have all conspired in recent years to quicken the pace of monarch butterfly decline in California and elsewhere. Even so, most monarch scientists don’t believe monarchs will become extinct.
“The migration won’t last forever. The monarchs will,” said migration expert Andy Davis, Assistant Research Scientist at the Odum School of Ecology at the The University of Georgia and editor of the journal, Animal Migration. “The monarchs will adapt just like they have in every other population around the world,” he said.
Davis recently shared news of several recent studies on monarchs on his educational MonarchScience blog, including one by Hannah Vander Zanden, an assistant professor at the University of Florida. Her research showed in a small sample that almost 40% of monarchs in Florida have migrated from the Midwest or elsewhere.
The Vander Zanden paper, “Alternate migration strategies of eastern monarch butterflies revealed by stable isotopes,” seems to upend what we thought we knew about the fall migration of eastern monarchs, wrote Davis. “We’ve always assumed that the winter destination of the eastern breeding population is the mountains of Central Mexico, but what if it isn’t? What if they don’t ALL travel to Mexico…what if over time, greater and greater numbers of monarchs are choosing to travel to these ‘alternate’ winter destinations, like South Florida? Wouldn’t that mean the Mexican overwintering colonies would slowly decline in size?”
The above video by Joel Moreno at JM’s Butterfly B&B shows the massive numbers at Cerro Pelón, part of the Monarch Butterfly Biosphere Preserve in the state of Mexico.
Perhaps, but not this year. The 2019 crop of monarch butterflies that roost in Mexico appears to be having its best year in a decade.
“We’ve had a set of dynamics in the east that were really, really good,” said Taylor.It’s still early in the season, and a freak freeze or catastrophic climate event could change everything, but monarch butterfly followers are hopeful of a huge rebound in the eastern migratory population this year. The official count won’t be released for several weeks, yet every indicator suggests the numbers of monarchs at the roosting sites in 2019 will be one of the biggest in a decade.
Scientists are cautiously optimistic about this year’s migratory eastern population. A freak storm like the one that occurred at Sierra Chincua could change everything. Photo by Dr. Isabel Ramíro
Taylor was so upbeat about the overwintering population, he encouraged readers of the much followed DPLEX list, an email community that closely tracks news of the migratory butterflies, to visit Mexico and see the rebound for themselves.
“In case you haven’t gotten the message, this is the year to visit the monarch colonies in Mexico,” Taylor wrote in late December, while sharing news of impressive butterfly numbers from visitors to the preserves. “The reports suggest that the overwintering population this year is the largest since 2008 and could even be larger than the 5.06 hectare population recorded that year. A population of this size may not occur again for another decade, and perhaps never, given the increasing temperatures in March and April that greet the monarchs returning from Mexico.”
Ellen Sharp, of JM’s Butterfly B&B, which sits at the entrance of the Cerro Pelón preserve near the small town of Macheros, Mexico, also chimed in about the big monarch numbers. “We’re having the most populous season in decades,” Sharp posted on Facebook.
What could explain the disparate numbers in monarch populations east and west?
“There’s pretty good evidence that they’re just not correlated,” said Oberhauser. “What goes on in the east is not connected to what goes on in the west because we have different weather patterns.”
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