09/08/2026
A little bit of history about how the monarch migration was discovered. Thank you, Shelb Green, for sharing this interesting information on your page.
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In January 1976, a monarch butterfly with a tag from Minnesota was found at a winter colony in the mountains of Mexico, roughly 1,750 miles from where it had been tagged four months earlier. On September 6, 1975, a schoolteacher named Jim Gilbert and two students from North Hopkins Junior High had tagged roughly 100 monarchs on a restored prairie at the University of Minnesota Landscape Arboretum in Chaska.
The morning started at 47 degrees. Monarchs cannot fly below 50. By 9 AM the air climbed past 55 and 200 monarchs lifted from the goldenrods and blazing stars and began visiting flowers across the 10-acre prairie. Gilbert, Jim Street, and Dean Boen netted them one at a time, pressed a small adhesive tag onto the right front wing of each butterfly, recorded the number, and released it. One of the tags read PS 397. Four months later it was in Mexico.
Fred Urquhart, an entomologist at the University of Toronto, had been searching for where North America's monarchs go in winter since the 1930s. He spent 25 years developing tagging methods, recruiting thousands of volunteers to tag butterflies across the continent, and following every lead south. Over 300,000 monarchs were tagged during that quarter century. He traveled over 100,000 miles. He visited 56 universities. He found monarchs wintering in the Caribbean, in Florida, along the Gulf Coast. He did not find the main colony.
In January 1975, Ken Brugger, an American living in Mexico, called Urquhart's office. His voice was shaking. We have found them, he said. Millions of monarchs, in evergreens beside a mountain clearing. Brugger and his wife Catalina had located the colony at roughly 10,000 feet in the volcanic mountains of Michoacán, in a forest of oyamel fir where the butterflies covered the trees so completely that the bark was invisible.
Urquhart was in his sixties and in declining health. It took him a year to make the trip. In January 1976, he and his wife Norah climbed the mountain with the Bruggers and a National Geographic photographer. At roughly 8,500 feet, they reached the colony. Millions of monarchs hung from the fir branches in clusters so dense that the weight bent the limbs toward the ground.
Then a branch broke. The weight of the butterflies snapped it from the trunk and it crashed to the forest floor, sending thousands of monarchs scattering across the ground. The photographer asked Urquhart to sit among them for a photograph. Urquhart sat down on the ground surrounded by fallen butterflies. He reached into the pile. He picked one up. It had a white tag on its right front wing. It read PS 397.
A butterfly tagged by a schoolteacher and two students at a prairie in Chaska, Minnesota, four months earlier. Roughly 1,750 miles from where Jim Gilbert had pressed the tag onto its wing on a September morning when the temperature was barely warm enough for the animal to fly.
Urquhart wrote to Gilbert immediately. I found it on January 18, 1976, in the overwintering colony in the volcanic mountains of Mexico at an altitude of approximately 8,500 feet, temperature about 34 degrees. He called it indisputable proof of an incredible journey.
The discovery was announced in the August 1976 issue of National Geographic.
Image is for illustration purposes only
Source: Jim Gilbert, Star Tribune / Three Rivers Park District / Fred and Norah Urquhart / National Geographic, August 1976 / Urquhart (1976), Journal of the Lepidopterists' Society / SDPB / Great Parks Blog.
