Chain Saw Thins Flocks of Migrants on Gold Wings

CONTEPEC, Mexico, March 9 – Homero Aridjis, a poet and naturalist, can remember years when monarch butterflies filled the streets here in his hometown like a living torrent of orange and black and stayed all winter on the fir-covered mountain rising above the village.

Not this year. The colony of butterflies that arrived here in November was tiny and retreated up the mountain, as far away as possible from the lower slopes where loggers have thinned or destroyed the forest the butterflies depend on.

Homero Aridjis, a poet and naturalist, helped set up the sanctuary to save the monarchs.

“There used to be rivers of butterflies, but now there are years when there are no butterflies at all,” Mr. Aridjis said as he climbed the mountain of his youth recently. “This is a village full of ghosts, not of people, but of nature, a paradise lost.”

The tourists still come, but there is not as much for them to see. This is a small town of 10,000, like many in Mexico, dominated by a church and a school in rolling fields at the foot of Cerro Altamirano. The country people here still work on their small farms, but in recent decades the town’s adobe houses have been replaced by uglier cinderblock buildings, and rusting automobiles outnumber burros and horses.

Not only are there comparatively few monarchs in Contepec, but the numbers that came to weather the winter at five other forest sanctuaries in central Mexico also dropped sharply this year.

Two storms killed most of the butterflies spending winter here in 2003 and 2004. But these reproductively hardy insects have bounced back before. In 2002, a storm killed about 80 percent of wintering butterflies, but the next summer, they found perfect breeding conditions in the central United States and southern Canada.

Last summer, though, cold and wet weather in the American corn belt kept the diminished population from regrouping. The number arriving this winter was the smallest since Mexico and the World Wildlife Fund began keeping records in the 1970’s, down three-quarters from the winter before, the wildlife fund and independent biologists said.

Miriam Vidal Ambrosio, 10, and a fluttering guest in the sanctuary created for monarch butterflies in Mexico’s Sierra Chincua.

Biologists and nature lovers say bad weather is not the whole story. They warn that logging in Mexico and herbicides in the United States have endangered these almost miraculously migratory insects, which flutter thousands of miles.

Hardier genetically altered corn and soybean crops in the United States and Canada, in the breadbasket areas that are the monarch’s main summer conjugal grounds, have enabled farmers to use stronger herbicides to eliminate weeds. That has drastically depleted the supply of flowers on which the butterflies feed, as well as common milkweed, on which the monarch lays its eggs in the spring and summer and on which its larvae feed, several biologists say.

The drop in butterfly counts is staggering. In 2004, at a monitoring site in Cape May, N.J., for instance, scientists registered the lowest number of butterflies heading to Mexico since the program began in 1991, according to scientists in the field. Similar results were found in Virginia. Scientists from the University of Minnesota who have been counting larvae in the Midwest since 1997 recorded their lowest numbers. Some environmentalists say that preventing permanent devastation of the monarch population might require concerted action by Mexico, the United States and Canada, though these countries have not put the issue on their foreign affairs agendas.

“We have a trinational crisis,” said Mr. Aridjis, who helped set up sanctuaries in Michoacán State for the butterflies in the 1980’s.

In August, as the days shorten, the last monarch generation hatched in the summer stops reproducing and goes into a sort of sexual hibernation. The monarchs fly south to the forested hills in Michoacán and the State of Mexico, where their ancestors have spent winter for millennia. There, they find the perfect balance of coolness and humidity to remain alive for several months, without laying eggs. In February, they mate. Finally, in March, they return to the southern United States to lay their fertilized eggs and die.

In Mexico, illegal logging in these protected forests has shrunk the monarchs’ habitat and forced the insects to higher elevations, where they are vulnerable to the cold. The government protects the forests with armed federal agents during winter, but large logging operations have continued to eat away at the dense stands of Oyamel fir trees here.

Satellite photos compiled by United States scientists show that vast numbers of trees in the 140,000-acre Monarch Butterfly Biosphere Reserve , 75 miles east of Mexico City, have been logged and carted out, often by armed gangs who pay off the authorities, people tracking the fate of the butterflies say. The northeast face of Cerro Pelón, one of the mountains in the core of the reserve and a former winter home of butterflies, is stripped of trees now.

Monarchs at a sanctuary in Contepec, Michoacán State, where they spend winters, will leave soon for the United States.

“The deforestation is increasing per year in each period we studied,” said Daniel A. Slayback, a United States scientist studying the butterflies who has compared satellite photos from 1976 through 2004. “Whatever measures the Mexicans are taking, they are totally ineffective.”

A group of 11 biologists who study the monarch concluded in a paper distributed Feb. 17, “Monarchs have proven resilient to many environmental stresses but the ongoing deterioration and loss of habitat in Mexico, the United States and Canada has the potential to drive the population below a level from which it can recover.”

Lincoln P. Brower, a biologist at Sweet Briar College in Virginia who is one of the world’s foremost Monarch specialists, said the population had been cut so severely that one more bad storm over the winter might have finished it. “I would say the monarch is in a precarious situation now,” he said.

One reason is poverty. Martin Uilshes Maya, 35, a farmer from Contepec who loves the butterflies, is typical of many people in the region. He said he had 10 acres of land to feed his wife and two children. He grows enough corn and wheat to make about $3,600 a year, but the need for firewood sometimes drives him and his neighbors into the forest.

“Clearly, we are destroying the forest, but that is what life is giving us,” he said sadly. “It’s a very beautiful phenomenon, the butterflies, that gives us so much life.”

“But,” he said, “we don’t have any way to make money off tourism.”

Photos Adriana Zehbrauskas
for The New York Times