New insights into monarch butterflies
Winter’s chill descends across the nation, distinct populations of monarch butterflies get urge to migrate.
When winter’s chill descends across the nation, two distinct populations of monarch butterflies get the urge to migrate: the eastern insects head to Mexico; the western insects flock to the California coast.
That’s the age-old dogma. And it’s wrong.
Emerging research shows that these spectacular migrations are linked by shared genes and behaviors, a finding that buoys hope for the resilience of the iconic species.
“This old ‘Berlin Wall’ model — that these butterflies are two different things, divided by the Rockies — is bankrupt,” said Robert Pyle, founder of the Xerces Society, at the first-ever Western Monarch Summit in Carmel last weekend.
It’s true that eastern monarchs fly south to Mexico in the winter — but when they reverse course in the spring, not everyone returns to the East. Some head to Arizona and California.
And not all western monarchs flock to the warm California coast. Some fly to Arizona and Mexico.
These migratory meetups likely explain another new discovery, revealed through the DNA sequencing of monarchs’ genomes: the two groups are very similar and likely belong to a single genetic population.
“A California monarch might mate with a monarch from Massachusetts and the monarch from Massachusetts goes back and lays eggs in Texas,” said insect ecologist Chip Taylor, founder and director of education, conservation, and research program Monarch Watch.
Monarchs’ spectacular long-distance migrations — an aerial dance of orange and black wings that’s part marathon, part relay race — have long fascinated scientists, who tag and study them in hopes of better understanding the biological basis of this behavior.
Unlike birds, this migration is multigenerational. Mysteriously, the insects arriving at their wintering grounds have never been there before. Rather, they are the descendents of insects that left months earlier and laid eggs along the way, breeding future generations who follow their own urge to move.
Both western and eastern populations are declining and scientists are scrambling to learn why. Much of the overwintering habitat has disappeared. Pesticide use, climate change, fierce storms and drought also take a toll. In the Bay Area and coastal California, they overwinter in clusters on eucalyptus trees. In early spring, they fan out to the Central Valley, Sierra Nevada, Washington, Oregon and beyond.
But for reasons no one yet fully knows, our butterflies are worse off than their eastern peers.