Wildlife experts call this a magical time of year as monarch butterflies have begun their migration from their northern breeding grounds to Central Mexico for the winter, with recent sightings in Wisconsin.
The journey takes about two and a half months with the arrival of the monarchs coinciding with a significant cultural holiday in Mexico known as Dia de Los Muertos, which honors passed loved ones.
Karen Oberhauser, professor emerita of entomology at the University of Wisconsin-Madison, said the celebration likely predates awareness of monarch migration but the serendipitous timing creates a meaningful connection.
"Out of this chrysalis that looks kind of dead, this beautiful butterfly breaks free of the bonds of the earth and flies," Oberhauser explained. "You can see why a lot of cultures see this as synonymous with rebirth, this whole process of metamorphosis."
Oberhauser noted monarchs fly during the day and roost at night. The migration is tracked through citizen sightings, with roosts sometimes containing hundreds or thousands of butterflies. People can aid monarchs' migration by creating habitats of milkweed and nectar sources where the butterflies can stop along the way.
Only those known as "super generation" monarchs, which live significantly longer than non-migrating monarchs, make the thousands of miles journey to the mountains of Mexico. Oberhauser pointed out they weigh about the same as a paper clip, so mortality is to be expected. She acknowledged exact figures of migration survival are difficult to measure, but researchers know only about 2% to 5% of eggs and caterpillars even make it to adulthood.
"This final generation, this 2% to 5%, has to migrate all the way to Mexico and come part way back," Oberhauser emphasized. "It’s really an incredible story of survival against incredible odds."
Oberhauser underscored monarchs primarily use day length rather than temperature as migration cues. Though climate change can affect migration conditions, with hot and dry temperatures being particularly detrimental.
She added there is evidence more monarchs are joining nonmigratory populations along the Gulf Coast instead of completing the full migration to Mexico, though most still make the complete journey.
