After a four-hour drive over winding mountain roads to reach a remote fir forest in the Mexican state of Michoacn, my kids, ages 5 and 7, needed to let off steam. They ran ahead of us up the mountainside, giggling and shouting. As we rounded a turn in the path, we gasped: Tens of millions of monarch butterflies were clinging to the branches of hundreds of towering oyamel, or fir trees.
There were so many of the creatures, weighing just one gram apiece, that the massive branches groaned under their weight. Just then, the sun emerged from behind a cloud, and the butterflies fluttered en masse into the air, creating a magnificent contrast of orange wing against azure sky. There was a sound of wind whistling through the trees; but no, that was the beating of millions of gossamer wings. Few things leave 5-year-old Colin speechless, but all he could mutter was: "Awesome!"
The monarch butterfly reserves in central Mexico represent a unique phenomenon of nature: Many butterflies migrate, but the monarch (Danaus plexippus) is the only variety whose migration spans several generations. Each fall, as many as one-half billion monarch butterflies in the Great Lakes region of Canada and the northern U.S. begin an arduous, 2,000-mile flight south into Mexico. Normally, in the summer months, a monarch lives only three to four weeks. But butterflies born at summer's end, in August or September, are fated to live 10 months and are mysteriously programmed to fly south.
The butterflies fly up to 80 miles a day at speeds of up to 30 mph, taking about a month to reach a volcanic mountain range in central Mexico, where they take refuge in cool fir forests, 9,000 feet above sea level. The semidormancy in which they spend the winter helps them conserve body fat and delays sexual maturity, extending their life span. By the time they start flying back north at the end of March, they have lived 10 months. En route, they lay their eggs on milkweed, and then die. Subsequent generations continue the voyage north, and in the fall, the cycle is repeated.
PETERED OUT. For nearly 40 years, Canadian zoologist Fred Urquhart tried to figure out where the monarchs flew each winter. He fixed minuscule numbered tags to their wings, asking the finder to call him. Over the years, he got calls from several U.S. states, but the trail always petered out in Texas. Finally, he got a few calls from Mexico, including one from a man who volunteered to search for the final destination of the butterflies.
On one foray in the winter of 1975, the man reached the tiny Michoacn farming town of Angangueo, about 150 miles west of Mexico City. "Where do all the butterflies go?" he asked townspeople. A shepherd led him to the same mountainside that my children and I visited 20 years later. When Urquhart first saw the site, he wept. But an immediate fear was that tens of thousands of visitors--like us--would flock to the site and destroy the fragile habitat.
Scientists believe that the monarch probably originated millions of years ago, in Mexico and other tropical areas. During the fluctuation of cold and warm cycles in the Pleistocene period, when the forest in eastern North Aeerica became much more temperate and boreal, the monarchs seem to have moved northward, following the milkweed plant, the seeds of which were transported to new climes by the retreating glaciers. Thus the monarch lives largely in Canada, the U.S., and Mexico. That fact was not lost on negotiators of the North American Free Trade Agreement, who unofficially adopted the monarch as a symbol of the new interdependence that open borders would bring.
For the monarch is, indeed, extremely dependent on trilateral cooperation. As more herbicides are used on Canadian and U.S. highway median strips and on farms, the milkweed on which the butterflies depend is eliminated. And in Mexico, indiscriminate logging is quickly shrinking the monarch's winter hideaways.
In 1986, under pressure from local and international environmentalists, the Mexican government set aside 40,250 acres of land in five designated sanctuaries where the butterflies gather each winter. Two areas were opened to the public. But each spring, when the butterflies start their long migration north, illegal logging begins again in the buffer zones surrounding the protected areas. When trees are removed, the winter temperatures drop more than usual, and the butterflies are exposed to humidity and rain that make them freeze. In 1992, during an especially cold winter, as many as 80% died.
BAD NEWS. University of Florida zoologist Lincoln P. Brower is studying the monarch to determine how the butterflies use a poisonous substance called digitoxin, found naturally in milkweed, to become inedible to most birds. Brower wants to know why monarchs are able to sustain such high concentrations of the toxin in their system; the same levels in humans would paralyze the heart. He also wants to know why two kinds of birds observed in Mexico seem to have developed an immunity to the digitoxin, and are able to eat the monarchs. Those studies could lead to the discovery of useful drugs.
Mexico's economic crisis could be bad news for the butterflies. As a deep recession sets in, the government may tolerate even more illegal logging in the mountains. That would be short-sighted. Already, communities around the butterfly reserves have increased their income by catering to ecotourists. If the forests disappear, so does that income.
In recent years, the government's "Lucrative Ecology" program has helped peasants build environmentally sound businesses, such as trout farms, brick factories, and textile concerns. Monarca, an environmental group in Mexico, has another idea: Set up a limited number of sawmills and furniture manufacturing concerns in the area, so that local residents can add value to the lumber they cut outside the buffer zones. While not without its risks, such a scheme could buy the butterflies--and their admirers--a few more years in paradise.