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Thousands Join in Tagging Wings

In 1952 I had written a magazine article on “Marked Monarchs,” which included an appeal for volunteers to assist in our tagging program. Twelve people responded, launching our Insect Migration Association. By 1971 it numbered six hundred; thousands have taken part over the past 24 years. The tiny labels carry identifying letters and numbers, and the words: “Send to Zoology University Toronto Canada.” Over the years hundreds of thousands of migrating monarchs have been tagged all across the continent. Reports have poured in from enthusiastic collaborators of all ages and walks of life. We have received tagged specimens from Maine and Ontario to California and Mexico, from Florida to the shores of Lake Superior.

Many tagged monarchs reached us alive, in packages lined with the field flowers they were feeding on when netted. A California golfer was about to drive his teed-up ball, when a butterfly alighted on it. Although unable to check his swing, he sent us the tagged remains in the name of science.

Early in 1965 I joined the staff of Scarborough College of the University of Toronto. Our program gained momentum. Grants in aid of our research came from the National Geographic Society, the National Research Council of Canada, and as donations from volunteer associates.

Our knowledge of the monarch proliferated as data flooded in. We learned, for example, that almost all males die on the way north from the wintering grounds. We also confirmed that the insects won’t fly at night. One tagged butterfly—captured, released, and captured again—flew 80 miles in one day.

During the summer in Ontario we found not only fresh, flawless monarchs; many were somewhat worn, and still others badly travel-tattered. This suggested several overlapping generations, the most worn having flown from farthest south, and the freshest having only recently hatched somewhere much closer on the northward migration route.

We also found that monarch populations include migrants and nonmigrants. What a fascinating complication this was!

After considerable study we concluded that most of the migrating monarchs are those that hatch in late summer, when daylight hours decline. The late females do not develop productive ovaries—and thus do not mate—until they fly south to that elusive overwintering place. (This light-responsive infertility probably holds for male monarchs as well.) As daylight lengthens in the wintering area, the monarchs—now sexually mature—feel the urge to mate and fly north, breeding new generations along the way.

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