National Geographic : 1972 Mar
step seemed to demand a decision. Where would my boot do the least damage? Alaska state regulations require that vehi cles stay off the tundra during summer's thaw, except for emergencies and scientific proj ects. Otherwise, ground transport is under taken only in winter, when the surface is frozen. Meanwhile, researchers conduct tests on shrubs and grasses from all over the Arctic world to determine which would be helpful if tundra reseeding proves practical. Other researchers investigate the strange ways evolved by tundra insects to assure the survival of their kind. "Here's one that has developed an astonish ing way to get its young through the first harsh winter," entomologist Mark Deyrup told me one day. He pointed to a pinned speci men he'd taken. "It's a warble fly, a fuzzy relative of the common housefly. It affixes its eggs to a caribou's abdominal hairs in the fall. The hatching larvae burrow into the skin and work their way into the back tissues. All through the winter, the larvae have a warm home inside the animal. By the time they work their way out through the skin, another tundra summer will have begun." Insects, food supply, weather, terrain, and the mating urge figure in the complex migra tion cycles of caribou, a subject only vaguely understood. Alaska's two northern herds, whose estimated 440,000 animals constitute two-thirds of the caribou in the state, move between the south side of the Brooks Range and the North Slope in a generally north south pattern. Pregnant cows go north in the spring to bear their calves on the tundra (pages 336-7), and the bulls follow. By fall the herds are back on the wooded south slopes of the Brooks Range for mating, and they remain all winter. But what would happen if massive herds met an oil pipeline on their northward jour ney? Would it divert them? Near Prudhoe Bay the oil industry built a two-mile stretch of four-foot fence to simu late a pipeline. At intervals ramps of earth al lowed passage over the barrier. Some sections were on a trestle, allowing passage below. Last summer about 1,000 animals con fronted the fence as they ambled in search of better grazing. Few went over or under it; those that did not retreat moved parallel to the fence until they could skirt one end hinting that an above-ground pipeline may in fact prove a serious barrier to migration. (Continued on page 313) 306 Oriented lakes by the thousands lie on a common northwest southeast axis, a phenomenon that intrigues scientists. Among possible causes under study are prevailing winds, which here blow from the northeast, at right angles to the lakes. Pingos As a tundra lake fills with silt, permafrost encroaches from the sides. At last sediments at the center become frozen; unable to expand sideways, excess water bulges upward as it freezes, forming an ice-cored mound, or pingo.