National Geographic : 2001 Jul
life cycle takes place on prairies, possibly as far away as Nebraska. By analyzing DNA from specimens, Robison hopes to pinpoint those locales, for reasons I soon learn. She hands me what looks like a chunk of glazed pottery found near the trap. Consisting of countless hard little legs compressed with shiny wing parts, it is-thanks very much-grizzly dung. "When the moths arrive in the high country during late June or early July, about 40 percent of their body weight is fat," she says. "By late August that has increased to 72 percent. They become the richest food in the ecosystem, with more calories per gram than elk or deer meat." The insects congregate at dozens of lofty Yel lowstone sites, where grizzlies roll the rock CROSSING TO SAFETY? Hunting, trapping, and habitat loss have confined North America's grizzlies to Canada, Alaska, and isolated pockets in the U.S. Northwest. Grizzlies roam huge home ranges but are reluctant to cross busy highways. Wildlife overpasses (left) in Alberta have been used by a handful of bears. rubble to get at them. Similar moth assemblies occur high in Montana and possibly Canada. Over the winter a large bear can lose 150 pounds, which needs to be replaced. Size and body fat affect how many cubs a female pro duces. For males, getting big means competing more successfully for mates. Observers have calculated that a silvertip can eat 2,500 moths an hour and 40,000 a day. A month of such steady feasting could fulfill nearly half the bear's energy requirements for the year. Not every area is that loaded with winged nougats, but the hot spots resemble a salmon stream, with as many as 23 grizzlies foraging together. Before Hicks and McQueary joined Robison, they were stringing lengths of barbed wire along streams flowing into Yellowstone Lake. More than 60 serve as cutthroat trout spawn ing areas. DNA from hairs snagged by the barbs has told of at least 80 grizzlies homing in on the fish. This is important to know because some lunkhead, who presumably wanted bigger fish to fry, dumped non-native .i ^~ ~~~* /C )~CI.rl Researchers estimate that roughly 25,000 brown bears still live in Canada. ,A I WSTONE IONALPARK 'Cody a . Fork *'fhi'wnv R. Meeteetse \ WYOMING Brown bear ecosystem l- su (estimated U.S. populations) The long-term survival of isolated National forest populations may depend on the creation of linkage zones-narrow om 10 oo National park strips of bear-friendly habitat that km 100 Wilderness would restore connections between SOURCE:CHRISTOPHER SERVHEEN, U.S.FISHANDWILDLIFESERVICE Potential linkage zone populations in the north and south. NATIONAL GEOGRAPHIC MAPS IAV 4-.