STEVE INSKEEP, HOST:
We cover so much news about the U.S.-Mexico border crossing that it is fitting that we also cover this. Border crossings have increased - crossings by monarch butterflies. The butterflies migrate north and south across the Americas, and Mexico's conservation efforts are paying off. Millions of monarch butterflies have made it back to winter in the forests of central Mexico, with numbers up a stunning 144 percent. NPR's Carrie Kahn reports from Mexico City.
CARRIE KAHN, BYLINE: Environmentalists burst into applause as this year's better-than-hoped-for monarch butterfly census figures were announced to a packed conference room.
KAHN: Andrew Rhodes, Mexico's commissioner for natural protected areas, says the migrating monarchs covered nearly 15 acres of pine and fir forests in the center of the country. Last year, that number was a little more than 6 acres.
ANDREW RHODES: (Speaking Spanish).
KAHN: "The amount of territory that filled this year gives us much hope for the future of the species," says Rhodes.
Mexico calculates the number of acres the butterflies inhabit instead of counting individuals. Researchers say they haven't seen this many butterflies return to Mexico in more than a decade. In fact, the numbers in recent years have been falling so dramatically that just five years ago, a little more than an acre of forest was covered with the insects.
Officials say the stellar census numbers are due in part to a successful crackdown on illegal logging in the monarchs' protected forest reserves. But Chip Taylor, an ecology professor at the University of Kansas and director of Monarch Watch, a butterfly tagging program, says it's too soon to celebrate one year's good numbers.
CHIP TAYLOR: In effect, we dodged a bullet this year. We had very, very good conditions. We can't expect that to happen again - perhaps never.
KAHN: He said last spring was an unusually cool one in Texas. The temperature shift gave the butterflies a few more weeks to hatch their eggs, increasing the entire migratory population's numbers. However, Taylor says climate change and increasingly warmer temperatures makes a repeat successful season highly unlikely.
And while he applauded efforts in the U.S. and Canada to plant more milkweed, the butterflies' food source, Taylor says it's nowhere enough to make up for the millions of acres of monarch habitat already lost to modern agriculture practices, roadside construction and pesticides.
Carrie Kahn, NPR News, Mexico City.
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