National Geographic : 2014 Nov
Wild Things EXPLORE Fewer monarch butterflies are crossing North America to winter in Mexico, says the World Wildlife Fund Mexico. In 2004 an estimated 550 million completed the winter migration; last season an estimated 33 million made it, according to the fund’s count. Although illegal deforestation and severe weather contributed to the decline, recent research suggests that the biggest culprit is farms’ large-scale use of herbicides that destroy milkweed. Monarch caterpillars need to feed on the plant—but it decreased 21 percent in the United States between 1995 and 2013. That doesn’t bode well for the butterflies, whose life span is so short that those making the next migration will be the great-grandchildren of the previous migra- tors. For this winged orange icon, survival is a group effort. —Lindsay N. Smith A Vanishing Migration Monarchs migrate up to 3,000 miles each fall to their wintering area in central Mexico. In the past few years citizen scientists have recorded a sharp drop in the number making the trip. SNAKING THEIR WAY HOME Move over, homing pigeons. When scientists in the Everglades radio-tagged and relocated invasive Burmese pythons, the snakes navigated up to 20 miles to return to their home turf. Biologist Shannon Pittman says the reptiles may steer using celestial cues. It’s bad news for South Florida if the snakes invade new areas, knowing they can always get home. —Christine Dell’Amore NGM MAPS. SOURCE: JOURNEY NORTH. PHOTOS: JOEL SARTORE; DON FARRALL, GETTY IMAGES (TOP) 0mi 400 0km 400 Wintering area Wintering area PACIFIC OCEAN ATLANTIC OCEAN Gulf of Mexico CANADA UNITED STATES MEXICO 2010 2013 Recorded overnight monarch roost sites Darker orange dots indicate multiple sites in the same locale.