for National Geographic News
Of all the churches I saw in Mexico, the forest of Sierra Chincua was most cathedral-like.
Its many-storied firs, each standing as slender and erect as the supports of a Gothic arch, rose gracefully skyward. Beneath them, I felt dwarfed and awed, the way a worshipper might in the nave of Mexico City's Basilica de Guadelupe.
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My friend Marc and I had left the capital just that morning and driven to these volcanic highlands in the central state of Michoacan. Now we found ourselves at an elevation of 10,000 feet (3,000 meters), working to keep pace with our guide, Gilberto, who led the way along a path that hugged the forested hillside.
As we penetrated more deeply into the forest, Gilberto told usrepeatedlyof the pains that he and others took to maintain its oyamel firs.
"He keeps saying how they plant saplings during the off-season," Marc translated. "It seems really important to himbecause he's really hammering the point home."
There's good reason for Gilberto's fixation with the trees. They support the butterflies. And the butterflies support him.
The butterflies of Sierra Chincua, or Chincua Hill, are monarchs. The flitting, orange-yellow-and-black insects found over much of the United States during summer months. In winter, nearly all North American members of the species congregate in a tiny region of Michoacan.
Each September, 100 million or more young monarchs begin the journey south. A couple of months and several thousand miles later, they home in on central Michoacan's oyamel forests. Here they and their progeny stay all winter, moving only slightly to change elevation as temperatures change.
In late February, the monarchs display a burst of reproductive passion. Impregnated females then depart for the north. The males die here.
Scientists believe that the monarchs have been repeating this cycleand making their annual pilgrimage to Sierra Chincua and a handful of neighboring hillsfor thousands of years.
The miracle of the monarchs' migration lies not only in the distance that the fragile animals cover, but also in the fact that no single butterfly knows the way from experience. Their lives span only a few months each, so the individuals that make the journey to Mexico are several generations removed from those who last left it.
To find their way back to their ancestral home, the monarchs use an internal compass set by the position of the sun in the sky. Scientists at the University of Massachusetts have recently discovered that the butterflies also use the sun to set circadian clocks that they need to properly orient themselves for their transit.
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