Mysterious Monarchs - the amazing mirgration of monarch butterflies

Animals, Jan, 2000 by Sy Montgomery

Unveiling secrets of a butterfly's magical migration.

When northerners are grabbing snow shovels and huddling against the wind, these insects cling to trees by the millions, overwintering on just 500 acres in Mexico and California. Their orange wings literally cover the boughs. But when the temperature begins to rise and signal spring, the monarchs know: it is time for their migration, the greatest butterfly spectacle on the planet.

Author and ecologist Robert Michael Pyle calls it "the sky river." Wave after wave of flapping orange-and-black butterflies begin to pour over the North American landscape, heading north at a rate of 40 to 100 miles per day. Their grandparents left their summer range the previous autumn; now, in spring, the sky river gives off another generation and then another and another, each of which lives just weeks. The sky river, Pyle explains, runs two ways: north with the spring, south with the fall.

All these beautiful, large butterflies share a common goal: they are all heading on a migration of hundreds or thousands of miles that none of them has ever before undertaken. How these featherlight insects accomplish this long-distance feat is a mystery that has tantalized naturalists for centuries.

Until recently, nearly everything about them was unknown. Where most of the monarchs--the majority of the population east of the Rockies--spend the winter, among forested slopes west of Mexico City, was only discovered in 1975, thanks to 40 years of butterfly tagging initiated by Fred Urquhart of Toronto and his collaborators. Debate still continues over the exact routes the insects take and how long the monarchs have been doing this (some say the trip is a response to post-settlement deforestation). One University of California biologist, Adrien Wenner, even contends they don't migrate; he argues they are merely expanding and contracting their range, as many other butterflies do. Naturalist and author Edwin Way Teale considered the migration of the monarch "one of the most puzzling features" of American seasons. Four decades later, Pyle writes, it puzzles still. "Confronted with thousands or millions of big, flapping, soaring, gliding, sucking creatures clearly going somewhere," he writes, "we stand in awe."

Lately, though, scientists have done much more than stand there. They have tracked monarchs with radar, subjected them to magnets and jet lag in experiments, and affixed millions of tiny tags to the insects' forewings in hopes of recovering them and learning their routes. Three autumns ago, Pyle decided to go one step further: he followed them. On foot and in his car, for 9,462 miles over $7 days, the Washington State ecologist traveled with monarchs from their northernmost breeding grounds in British Columbia down to their wintering grounds in Mexico and California.

His chronicle of the experience, Chasing Monarchs: Migrating with the Butterflies of Passage, published last Fall, comes on the heels of startling new discoveries about the monarchs' migration--and the threats to their survival. Despite two decades of international proclamations calling for their protection, America's most beloved butterflies are under siege. Threats range from illegal logging in their Mexican wintering grounds to toxic pollen from gene-spliced corn to a trendy new way to celebrate weddings.

Says Pyle, "The migratory butterflies are in worse trouble than ever." On his two-month journey, he saw many of these threats firsthand. He bedded down with the insects and rose with them. As they floated on thermals, he followed below in his 1982 Honda, named Powdermilk. Sometimes he lost them in butterfly-barren landscapes, where pesticides poison their primary food plants, the milkweeds. When he lost track of them, he would head in the direction in which the last one he had seen had vanished. He watched them dodge swallows and dragonflies, saw them hit by cars. But he also observed in these delicate-looking insects an astonishing resiliency, plasticity, and individuality, and something that, if it were observed in humans, could only be called an iron will.

"As I watched this perfect monarch steadying herself to sail on," he writes of one butterfly he observed, "facing a journey of 1,000 miles or more, I had to believe that there was a little more of something like freedom built into her system than the rigid lines drawn on migration maps seem to allow. Nothing so refined as freedom as we think of it ... but the freedom, nonetheless, to respond to the vagaries and gifts of the days with every adaptive tool and option that kindly evolution has provided."

Ingenious experiments are now revealing how migrating monarchs use these adaptive tools. For, although butterflies can and do learn--Pyle has seen them learn and remember the exact location of individual nectar plants--this ability can't help them find their way to a place none of them has ever been before. Few, if any, ever make it back to their birthplace in the spring, and none survives to make the trip south again in the fall.