- Associated Press - Monday, August 16, 2010

MEXICO CITY (AP) - The number of Monarch butterflies wintering in western Mexico has plunged despite a dramatic decline in illegal logging in their mountain forest nesting grounds, experts said Monday.

Factors including climate change, droughts and other extreme weather, and pesticide use north of the border are possible reasons behind the steep drop in the number of butterflies that arrived in Mexico following their annual long-distance migration from Canada and the United States.

Mexico has long been urged to fight illegal logging in the butterfly’s reserve and has recently strengthened enforcement in a bid to protect the butterfly.

A study of aerial digital photos taken over the butterfly’s reserve this winter _ roughly between November 2009 and February 2010 _ showed that only about 1.5 hectares (3.7 acres) of pine and fir forest were lost to loggers in the last year, down 97 percent from the previous year. At its peak in 2005, logging devastated as many as 461 hectares (1,140 acres) annually _ 300 times this year’s level.

A combination of enforcement of anti-logging laws, donations by private foundations and conservation groups to the communities that live within the reserve, and a greater consciousness of the forest’s value among the largely Indian population are responsible for the turnaround, experts say.

“They have realized that there are more benefits from preserving the forest, from tourism and tree nurseries … than there is cutting it down,” said Omar Vidal, Mexico director of the WWF.

The mountainous area west of Mexico City where the orange-and-black Monarchs spend the winter was once dotted by small, illegal lumber mills, many of which have been closed down by police.

In a little-understood phenomenon, the Monarchs migrate south each year by the thousands in tree branches to conserve heat. The trees provide a protective canopy against cold winds and rains.

But counteracting the benefits of reduced logging has been an increase in forest damage from extreme weather patterns. The area damaged by weather increased from almost nothing in previous years to about 177 hectares (437 acres) of the 13,550 hectares (33,482 acres) in the most recent season.

Most of the weather-related damage was from winds or mudslides that knocked down trees, though forest fires played a smaller role.

Park officials say a drought in early 2009 also weakened the trees, and a bark beetles infestation affected about 100 hectares.

And the overall number of butterflies wintering in Mexico has dropped steeply.

The WWF study, conducted with aid of Mexico’s National Autonomous University’s Geophysics Institute, indicated that only about one-fourth as many butterflies came to Mexico this winter as in the preceding year.

Vidal said the clusters of butterflies covered a total area equal to only about 1.9 hectares (4.7 acres) this year, compared to about 8 hectares (almost 20 acres) in the 2008-2009 winter season.

Rosendo Caro, the director of the reserve, agreed the butterflies had declined, but only to one-third of their former numbers, in part because he starts from a lower estimate of about 5.8 hectares of butterflies for the 2008-2009 season. But he said “this is the lowest number of butterflies in the last 17 years.”

Vidal says droughts in 2008 could have affected the butterflies in their summer range in the U.S. and Canada, decreasing the number of descendants who make the return trip to Mexico. No butterfly lives through the complete migration cycle.

“What happened to them? You would have to ask our colleagues in the United States and Canada what happened up there,” Caro said.

While Vidal notes that “climate change has severe impacts on Monarch butterflies,” he says pesticide use and development on former farm lands north of the border may also have an effect.

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