National Geographic : 2004 Sep
IAt some point, as temperatures continue to rise, species will have no more room to run. pairs in 1974 to 47 today. Fraser knew the Adlies had not migrated elsewhere, as his team had banded 20,000 penguins, only a few of which were found in other locations. But Fraser also knew that Adelies were being affected by more than local conditions, for even colonies in relatively snow-free spots were shrink ing. Larger forces were at work, and sea ice-vital to the Antarctic ecosystem-was at the heart of the matter. Adelies depend on sea ice as a feed ing and resting platform. The gentoo penguins that are replacing them thrive in open water. Sea ice on the western Antarctic Peninsula has declined by about 20 percent, depriving the Adelies of important jumping-off points for rich winter feeding grounds. Fraser continues to make important field observations. He discovered recently that Ant arctic silverfish-once an important food for Adelies-have disappeared from the Palmer Station area and are now found only in colder waters farther south. He also has documented an invasion of fur seals, a subantarctic mam mal, from areas such as South Georgia Island, 1,400 miles to the northeast. In 1974 Fraser counted six fur seals on the islands surround ing Palmer Station. Last summer he and his team saw 3,000. In effect, over three decades, Fraser and his col leagues have recorded the retreat of an Antarctic ecosystem. In Fraser's words: "It has gone to hell." A t the top of the world, in the Arctic, climate change is occurring swiftly as well, and animals and birds appear to be feeling the effects. As temperatures have risen across the Arctic, permanent sea ice has declined by 9 percent per decade since 1978, when satellite monitoring of the ice cover began. In Hudson Bay the summer sea ice breakup now generally occurs two to three weeks earlier than it did during the mid-20th century. For animals that spend most of their year living and feeding on the ice-notably 48 NATIONAL GEOGRAPHIC * SEPTEMBER 2004 polar bears and ringed seals-the continuing loss of sea ice could be disastrous. Last September I joined Martyn Obbard, a wildlife research scientist with the Ontario Ministry of Natural Resources, on the shores of southern Hudson Bay. An estimated 1,000 polar bears inhabit this region at the southern edge of the species' range in North America. Obbard, accompanied by veterinarian and fellow biologist Marc Cattet, was in the final year of a four-year project to weigh, measure, and take physiological samples from roughly 300 bears. Obbard would compare his measurements with those taken by biologists in the same region two decades ago. If polar bears are being forced to abandon the ice two to three weeks earlier than in the 1980s-departing at a time when they traditionally gorge on ringed seal UTAH(ABOVE);EL ROSARIOPRESERVE,MICHOACANSTATE.MEXICO(RIGHT) Heights of Vulnerability Freezing temperatures and more precipitation proved a lethal combination for millions of monarch butterflies in Mexico's mountains in early 2000. More such weather is projected. Cold-loving pikas in North America could face extinction if temperatures keep rising, driving the heat-sensitive mammals uphill to summits that effectively become shrinking islands of habitat.